src/test/java/io/reactivex/rxjava4/testsupport/TestHelper.java - 4.x - githubmirror/RxJava

src/test/java/io/reactivex/rxjava4/testsupport/TestHelper.java
3 885 строк128 KB
David Karnok
4.x: Streamable: +delay +timeout +zip +onErrorResumeNext, cleanup (#8216)
06 июл 2026, 00:10
06 июл 2026, 00:1079a67f1
/*
 * Copyright (c) 2016-present, RxJava Contributors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is
 * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
 * the License for the specific language governing permissions and limitations under the License.
 */

package io.reactivex.rxjava4.testsupport;

import static org.junit.jupiter.api.Assertions.*;
import static org.mockito.ArgumentMatchers.any;
import static org.mockito.Mockito.mock;

import java.io.*;
import java.lang.management.*;
import java.lang.reflect.*;
import java.net.URL;
import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.Flow.*;
import java.util.concurrent.atomic.AtomicInteger;

import org.mockito.Mockito;
import org.mockito.stubbing.Answer;

import io.reactivex.rxjava4.annotations.*;
import io.reactivex.rxjava4.core.*;
import io.reactivex.rxjava4.core.Observable;
import io.reactivex.rxjava4.core.Observer;
import io.reactivex.rxjava4.disposables.*;
import io.reactivex.rxjava4.exceptions.*;
import io.reactivex.rxjava4.functions.Function;
import io.reactivex.rxjava4.internal.operators.completable.CompletableToFlowable;
import io.reactivex.rxjava4.internal.operators.maybe.MaybeToFlowable;
import io.reactivex.rxjava4.internal.operators.single.SingleToFlowable;
import io.reactivex.rxjava4.internal.subscriptions.*;
import io.reactivex.rxjava4.internal.util.ExceptionHelper;
import io.reactivex.rxjava4.observers.BaseTestConsumer;
import io.reactivex.rxjava4.operators.*;
import io.reactivex.rxjava4.parallel.ParallelFlowable;
import io.reactivex.rxjava4.plugins.RxJavaPlugins;
import io.reactivex.rxjava4.processors.PublishProcessor;
import io.reactivex.rxjava4.schedulers.Schedulers;
import io.reactivex.rxjava4.subjects.Subject;
import io.reactivex.rxjava4.subscribers.TestSubscriber;

/**
 * Common methods for helping with tests.
 */
public enum TestHelper {
    ;

    /**
     * Number of times to loop a {@link #race(Runnable, Runnable)} invocation
     * by default.
     */
    public static final int RACE_DEFAULT_LOOPS = 2500;

    /**
     * Number of times to loop a {@link #race(Runnable, Runnable)} invocation
     * in tests with race conditions requiring more runs to check.
     */
    public static final int RACE_LONG_LOOPS = 10000;

    public static List<Throwable> trackPluginErrors() {
        final List<Throwable> list = Collections.synchronizedList(new ArrayList<>());

        RxJavaPlugins.setErrorHandler(list::add);

        return list;
    }

    /**
     * Mocks a subscriber and prepares it to request {@link Long#MAX_VALUE}.
     * @param <T> the value type
     * @return the mocked subscriber
     */
    @SuppressWarnings("unchecked")
    public static <T> FlowableSubscriber<T> mockSubscriber() {
        FlowableSubscriber<T> w = mock(FlowableSubscriber.class);

        Mockito.doAnswer((Answer<Object>) a -> {
            Subscription s = a.getArgument(0);
            s.request(Long.MAX_VALUE);
            return null;
        }).when(w).onSubscribe(any());

        return w;
    }

    /**
     * Mocks an Observer with the proper receiver type.
     * @param <T> the value type
     * @return the mocked observer
     */
    @SuppressWarnings("unchecked")
    public static <T> Observer<T> mockObserver() {
        return mock(Observer.class);
    }

    /**
     * Mocks an MaybeObserver with the proper receiver type.
     * @param <T> the value type
     * @return the mocked observer
     */
    @SuppressWarnings("unchecked")
    public static <T> MaybeObserver<T> mockMaybeObserver() {
        return mock(MaybeObserver.class);
    }

    /**
     * Mocks an SingleObserver with the proper receiver type.
     * @param <T> the value type
     * @return the mocked observer
     */
    @SuppressWarnings("unchecked")
    public static <T> SingleObserver<T> mockSingleObserver() {
        return mock(SingleObserver.class);
    }

    /**
     * Mocks an CompletableObserver.
     * @return the mocked observer
     */
    public static CompletableObserver mockCompletableObserver() {
        return mock(CompletableObserver.class);
    }

    /**
     * Validates that the given class, when forcefully instantiated throws
     * an IllegalArgumentException("No instances!") exception.
     * @param clazz the class to test, not null
     */
    public static void checkUtilityClass(Class<?> clazz) {
        try {
            Constructor<?> c = clazz.getDeclaredConstructor();

            c.setAccessible(true);

            try {
                c.newInstance();
                fail("Should have thrown InvocationTargetException(IllegalStateException)");
            } catch (InvocationTargetException ex) {
                assertEquals("No instances!", ex.getCause().getMessage());
            }
        } catch (Exception ex) {
            AssertionError ae = new AssertionError(ex.toString());
            ae.initCause(ex);
            throw ae;
        }
    }

    public static void assertError(List<Throwable> list, int index, Class<? extends Throwable> clazz) {
        Throwable ex = list.get(index);
        if (!clazz.isInstance(ex)) {
            AssertionError err = new AssertionError(clazz + " expected but got " + list.get(index));
            err.initCause(list.get(index));
            throw err;
        }
    }

    public static void assertUndeliverable(List<Throwable> list, int index, Class<? extends Throwable> clazz) {
        Throwable ex = list.get(index);
        if (!(ex instanceof UndeliverableException)) {
            AssertionError err = new AssertionError("Outer exception UndeliverableException expected but got " + list.get(index));
            err.initCause(list.get(index));
            throw err;
        }
        ex = ex.getCause();
        if (!clazz.isInstance(ex)) {
            AssertionError err = new AssertionError("Inner exception " + clazz + " expected but got " + list.get(index));
            err.initCause(list.get(index));
            throw err;
        }
    }

    public static void assertError(List<Throwable> list, int index, Class<? extends Throwable> clazz, String message) {
        Throwable ex = list.get(index);
        if (!clazz.isInstance(ex)) {
            AssertionError err = new AssertionError("Type " + clazz + " expected but got " + ex);
            err.initCause(ex);
            throw err;
        }
        if (!Objects.equals(message, ex.getMessage())) {
            AssertionError err = new AssertionError("Message " + message + " expected but got " + ex.getMessage());
            err.initCause(ex);
            throw err;
        }
    }

    public static void assertUndeliverable(List<Throwable> list, int index, Class<? extends Throwable> clazz, String message) {
        Throwable ex = list.get(index);
        if (!(ex instanceof UndeliverableException)) {
            AssertionError err = new AssertionError("Outer exception UndeliverableException expected but got " + list.get(index));
            err.initCause(list.get(index));
            throw err;
        }
        ex = ex.getCause();
        if (!clazz.isInstance(ex)) {
            AssertionError err = new AssertionError("Inner exception " + clazz + " expected but got " + list.get(index));
            err.initCause(list.get(index));
            throw err;
        }
        if (!Objects.equals(message, ex.getMessage())) {
            AssertionError err = new AssertionError("Message " + message + " expected but got " + ex.getMessage());
            err.initCause(ex);
            throw err;
        }
    }

    public static void assertError(TestObserverEx<?> to, int index, Class<? extends Throwable> clazz) {
        Throwable ex = to.errors().getFirst();
        try {
            if (ex instanceof CompositeException ce) {
                List<Throwable> cel = ce.getExceptions();
                assertTrue(clazz.isInstance(cel.get(index)), cel.get(index).toString());
            } else {
                fail(ex.toString() + ": not a CompositeException");
            }
        } catch (AssertionError e) {
            ex.printStackTrace();
            throw e;
        }
    }

    public static void assertError(TestSubscriberEx<?> ts, int index, Class<? extends Throwable> clazz) {
        Throwable ex = ts.errors().getFirst();
        if (ex instanceof CompositeException ce) {
            List<Throwable> cel = ce.getExceptions();
            assertTrue(clazz.isInstance(cel.get(index)), cel.get(index).toString());
        } else {
            fail(ex.toString() + ": not a CompositeException");
        }
    }

    public static void assertError(TestObserverEx<?> to, int index, Class<? extends Throwable> clazz, String message) {
        Throwable ex = to.errors().getFirst();
        if (ex instanceof CompositeException ce) {
            List<Throwable> cel = ce.getExceptions();
            assertTrue(clazz.isInstance(cel.get(index)), cel.get(index).toString());
            assertEquals(message, cel.get(index).getMessage());
        } else {
            fail(ex.toString() + ": not a CompositeException");
        }
    }

    public static void assertError(TestSubscriberEx<?> ts, int index, Class<? extends Throwable> clazz, String message) {
        Throwable ex = ts.errors().getFirst();
        if (ex instanceof CompositeException ce) {
            List<Throwable> cel = ce.getExceptions();
            assertTrue(clazz.isInstance(cel.get(index)), cel.get(index).toString());
            assertEquals(message, cel.get(index).getMessage());
        } else {
            fail(ex.toString() + ": not a CompositeException");
        }
    }

    /**
     * Verify that a specific enum type has no enum constants.
     * @param <E> the enum type
     * @param e the enum class instance
     */
    public static <E extends Enum<E>> void assertEmptyEnum(Class<E> e) {
        assertEquals(0, e.getEnumConstants().length);

        try {
            try {
                Method m0 = e.getDeclaredMethod("values");

                Object[] a = (Object[])m0.invoke(null);
                assertEquals(0, a.length);

                Method m = e.getDeclaredMethod("valueOf", String.class);

                m.invoke("INSTANCE");
                fail("Should have thrown!");
            } catch (InvocationTargetException | IllegalAccessException ex) {
                fail(ex.toString());
            } catch (IllegalArgumentException ex) {
                // we expected this
            }
        } catch (NoSuchMethodException ex) {
            fail(ex.toString());
        }
    }

    /**
     * Assert that by consuming the Publisher with a bad request amount, it is
     * reported to the plugin error handler promptly.
     * @param source the source to consume
     */
    public static void assertBadRequestReported(Publisher<?> source) {
        List<Throwable> list = trackPluginErrors();
        try {
            final CountDownLatch cdl = new CountDownLatch(1);

            source.subscribe(new FlowableSubscriber<Object>() /* NFI */ {

                @Override
                public void onSubscribe(Subscription s) {
                    try {
                        s.request(-99);
                        s.cancel();
                        s.cancel();
                    } finally {
                        cdl.countDown();
                    }
                }

                @Override
                public void onNext(Object t) {

                }

                @Override
                public void onError(Throwable t) {

                }

                @Override
                public void onComplete() {

                }

            });

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS));
            } catch (InterruptedException ex) {
                throw new AssertionError(ex.getMessage());
            }

            assertTrue(list.getFirst() instanceof IllegalArgumentException, list.toString());
            assertEquals(list.getFirst().getMessage(), "n > 0 required but it was -99");
        } finally {
            RxJavaPlugins.setErrorHandler(null);
        }
    }

    /**
     * Assert that by consuming the Publisher with a bad request amount, it is
     * reported to the plugin error handler promptly.
     * @param source the source to consume
     */
    public static void assertBadRequestReported(ParallelFlowable<?> source) {
        List<Throwable> list = trackPluginErrors();
        try {
            final CountDownLatch cdl = new CountDownLatch(1);

            var bad = new FlowableSubscriber<>() /* NFI */ {

                @Override
                public void onSubscribe(Subscription s) {
                    try {
                        s.request(-99);
                        s.cancel();
                        s.cancel();
                    } finally {
                        cdl.countDown();
                    }
                }

                @Override
                public void onNext(Object t) {

                }

                @Override
                public void onError(Throwable t) {

                }

                @Override
                public void onComplete() {

                }

            };

            @SuppressWarnings("unchecked")
            FlowableSubscriber<Object>[] subs = new FlowableSubscriber[source.parallelism()];
            subs[0] = bad;
            for (int i = 1; i < subs.length; i++) {
                subs[i] = NoOpConsumer.INSTANCE;
            }
            source.subscribe(subs);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS));
            } catch (InterruptedException ex) {
                throw new AssertionError(ex.getMessage());
            }

            assertTrue(list.getFirst() instanceof IllegalArgumentException, list.toString());
            assertEquals("n > 0 required but it was -99", list.getFirst().getMessage());
        } finally {
            RxJavaPlugins.setErrorHandler(null);
        }
    }

    /**
     * Synchronizes the execution of two runnables (as much as possible)
     * to test race conditions.
     * <p>The method blocks until both have run to completion.
     * @param r1 the first runnable
     * @param r2 the second runnable
     * @see #RACE_DEFAULT_LOOPS
     * @see #RACE_LONG_LOOPS
     */
    public static void race(final Runnable r1, final Runnable r2) {
        race(r1, r2, Schedulers.single());
    }
    /**
     * Synchronizes the execution of two runnables (as much as possible)
     * to test race conditions.
     * <p>The method blocks until both have run to completion.
     * @param r1 the first runnable
     * @param r2 the second runnable
     * @param s the scheduler to use
     * @see #RACE_DEFAULT_LOOPS
     * @see #RACE_LONG_LOOPS
     */
    public static void race(final Runnable r1, final Runnable r2, Scheduler s) {
        final AtomicInteger count = new AtomicInteger(2);
        final CountDownLatch cdl = new CountDownLatch(2);

        final Throwable[] errors = { null, null };

        s.scheduleDirect(() -> {
            if (count.decrementAndGet() != 0) {
                while (count.get() != 0) { }
            }

            try {
                try {
                    r1.run();
                } catch (Throwable ex) {
                    errors[0] = ex;
                }
            } finally {
                cdl.countDown();
            }
        });

        if (count.decrementAndGet() != 0) {
            while (count.get() != 0) { }
        }

        try {
            try {
                r2.run();
            } catch (Throwable ex) {
                errors[1] = ex;
            }
        } finally {
            cdl.countDown();
        }

        try {
            if (!cdl.await(5, TimeUnit.SECONDS)) {
                throw new AssertionError("The wait timed out!");
            }
        } catch (InterruptedException ex) {
            throw new RuntimeException(ex);
        }
        if (errors[0] != null && errors[1] == null) {
            throw ExceptionHelper.wrapOrThrow(errors[0]);
        }

        if (errors[0] == null && errors[1] != null) {
            throw ExceptionHelper.wrapOrThrow(errors[1]);
        }

        if (errors[0] != null && errors[1] != null) {
            throw new CompositeException(errors);
        }
    }

    /**
     * Cast the given Throwable to CompositeException and returns its inner
     * Throwable list.
     * @param ex the target Throwable
     * @return the list of Throwables
     */
    public static List<Throwable> compositeList(Throwable ex) {
        if (ex instanceof UndeliverableException) {
            ex = ex.getCause();
        }
        return ((CompositeException)ex).getExceptions();
    }

    /**
     * Assert that the offer methods throw UnsupportedOperationExcetpion.
     * @param q the queue implementation
     */
    public static void assertNoOffer(SimpleQueue<?> q) {
        try {
            q.offer(null);
            fail("Should have thrown!");
        } catch (UnsupportedOperationException ex) {
            // expected
        }
        try {
            q.offer(null, null);
            fail("Should have thrown!");
        } catch (UnsupportedOperationException ex) {
            // expected
        }
    }

    @SuppressWarnings("unchecked")
    public static <E extends Enum<E>> void checkEnum(Class<E> enumClass) {
        try {
            Method m = enumClass.getMethod("values");
            m.setAccessible(true);
            Method e = enumClass.getMethod("valueOf", String.class);
            m.setAccessible(true);

            for (Enum<E> o : (Enum<E>[])m.invoke(null)) {
                assertSame(o, e.invoke(null, o.name()));
            }

        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        }
    }

    /**
     * Calls onSubscribe twice and checks if it doesn't affect the first Subscription while
     * reporting it to plugin error handler.
     * @param subscriber the target
     */
    public static void doubleOnSubscribe(Subscriber<?> subscriber) {
        List<Throwable> errors = trackPluginErrors();
        try {
            BooleanSubscription s1 = new BooleanSubscription();

            subscriber.onSubscribe(s1);

            BooleanSubscription s2 = new BooleanSubscription();

            subscriber.onSubscribe(s2);

            assertFalse(s1.isCancelled());

            assertTrue(s2.isCancelled());

            assertError(errors, 0, IllegalStateException.class, "Subscription already set!");
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Calls onSubscribe twice and checks if it doesn't affect the first Disposable while
     * reporting it to plugin error handler.
     * @param observer the target
     */
    public static void doubleOnSubscribe(Observer<?> observer) {
        List<Throwable> errors = trackPluginErrors();
        try {
            Disposable d1 = Disposable.empty();

            observer.onSubscribe(d1);

            Disposable d2 = Disposable.empty();

            observer.onSubscribe(d2);

            assertFalse(d1.isDisposed());

            assertTrue(d2.isDisposed());

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Calls onSubscribe twice and checks if it doesn't affect the first Disposable while
     * reporting it to plugin error handler.
     * @param observer the target
     */
    public static void doubleOnSubscribe(SingleObserver<?> observer) {
        List<Throwable> errors = trackPluginErrors();
        try {
            Disposable d1 = Disposable.empty();

            observer.onSubscribe(d1);

            Disposable d2 = Disposable.empty();

            observer.onSubscribe(d2);

            assertFalse(d1.isDisposed());

            assertTrue(d2.isDisposed());

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Calls onSubscribe twice and checks if it doesn't affect the first Disposable while
     * reporting it to plugin error handler.
     * @param observer the target
     */
    public static void doubleOnSubscribe(CompletableObserver observer) {
        List<Throwable> errors = trackPluginErrors();
        try {
            Disposable d1 = Disposable.empty();

            observer.onSubscribe(d1);

            Disposable d2 = Disposable.empty();

            observer.onSubscribe(d2);

            assertFalse(d1.isDisposed());

            assertTrue(d2.isDisposed());

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Calls onSubscribe twice and checks if it doesn't affect the first Disposable while
     * reporting it to plugin error handler.
     * @param observer the target
     */
    public static void doubleOnSubscribe(MaybeObserver<?> observer) {
        List<Throwable> errors = trackPluginErrors();
        try {
            Disposable d1 = Disposable.empty();

            observer.onSubscribe(d1);

            Disposable d2 = Disposable.empty();

            observer.onSubscribe(d2);

            assertFalse(d1.isDisposed());

            assertTrue(d2.isDisposed());

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Makes sure the given {@link Disposable} is not disposed upfront,
     * disposes it, checks if it got disposed and then double checks
     * if disposing it again will not result in errors or no longer being disposed.
     * <p>
     * A common use for it is to make sure the {@link Disposable#isDisposed()} gets
     * covered even though naturally nothing would invoke that method in a normal flow.
     * @param d the {@code Disposable} to check
     */
    public static void checkDisposed(Disposable d) {
        assertFalse(d.isDisposed(), "Disposed upfront?!");

        d.dispose();

        assertTrue(d.isDisposed(), "Not disposed?!");

        d.dispose();

        assertTrue(d.isDisposed(), "Not disposed again?!");
    }

    /**
     * Checks if the upstream's Subscription sent through the onSubscribe reports
     * isCancelled properly before and after calling dispose.
     * @param <T> the input value type
     * @param source the source to test
     */
    public static <T> void checkDisposed(Flowable<T> source) {
        final TestSubscriber<Object> ts = new TestSubscriber<>(0L);
        source.subscribe(new FlowableSubscriber<Object>() /* NFI */ {
            @Override
            public void onSubscribe(Subscription s) {
                ts.onSubscribe(new BooleanSubscription());

                s.cancel();

                s.cancel();
            }

            @Override
            public void onNext(Object t) {
                ts.onNext(t);
            }

            @Override
            public void onError(Throwable t) {
                ts.onError(t);
            }

            @Override
            public void onComplete() {
                ts.onComplete();
            }
        });
        ts.assertEmpty();
    }
    /**
     * Checks if the upstream's Disposable sent through the onSubscribe reports
     * isDisposed properly before and after calling dispose.
     * @param source the source to test
     */
    public static void checkDisposed(Maybe<?> source) {
        final Boolean[] b = { null, null };
        final CountDownLatch cdl = new CountDownLatch(1);
        source.subscribe(new MaybeObserver<Object>() /* NFI */ {

            @Override
            public void onSubscribe(Disposable d) {
                try {
                    b[0] = d.isDisposed();

                    d.dispose();

                    b[1] = d.isDisposed();

                    d.dispose();
                } finally {
                    cdl.countDown();
                }
            }

            @Override
            public void onSuccess(Object value) {
                // ignored
            }

            @Override
            public void onError(Throwable e) {
                // ignored
            }

            @Override
            public void onComplete() {
                // ignored
            }
        });

        try {
            assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
        } catch (InterruptedException ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        }

        assertEquals(false, b[0], "Reports disposed upfront?");
        assertEquals(true, b[1], "Didn't report disposed after?");
    }

    /**
     * Checks if the upstream's Disposable sent through the onSubscribe reports
     * isDisposed properly before and after calling dispose.
     * @param source the source to test
     */
    public static void checkDisposed(Observable<?> source) {
        final Boolean[] b = { null, null };
        final CountDownLatch cdl = new CountDownLatch(1);
        source.subscribe(new Observer<Object>() /* NFI */ {

            @Override
            public void onSubscribe(Disposable d) {
                try {
                    b[0] = d.isDisposed();

                    d.dispose();

                    b[1] = d.isDisposed();

                    d.dispose();
                } finally {
                    cdl.countDown();
                }
            }

            @Override
            public void onNext(Object value) {
                // ignored
            }

            @Override
            public void onError(Throwable e) {
                // ignored
            }

            @Override
            public void onComplete() {
                // ignored
            }
        });

        try {
            assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
        } catch (InterruptedException ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        }

        assertEquals(false, b[0], "Reports disposed upfront?");
        assertEquals(true, b[1], "Didn't report disposed after?");
    }

    /**
     * Checks if the upstream's Disposable sent through the onSubscribe reports
     * isDisposed properly before and after calling dispose.
     * @param source the source to test
     */
    public static void checkDisposed(Single<?> source) {
        final Boolean[] b = { null, null };
        final CountDownLatch cdl = new CountDownLatch(1);
        source.subscribe(new SingleObserver<Object>() /* NFI */ {

            @Override
            public void onSubscribe(Disposable d) {
                try {
                    b[0] = d.isDisposed();

                    d.dispose();

                    b[1] = d.isDisposed();

                    d.dispose();
                } finally {
                    cdl.countDown();
                }
            }

            @Override
            public void onSuccess(Object value) {
                // ignored
            }

            @Override
            public void onError(Throwable e) {
                // ignored
            }
        });

        try {
            assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
        } catch (InterruptedException ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        }

        assertEquals(false, b[0], "Reports disposed upfront?");
        assertEquals(true, b[1], "Didn't report disposed after?");
    }

    /**
     * Checks if the upstream's Disposable sent through the onSubscribe reports
     * isDisposed properly before and after calling dispose.
     * @param source the source to test
     */
    public static void checkDisposed(Completable source) {
        final Boolean[] b = { null, null };
        final CountDownLatch cdl = new CountDownLatch(1);
        source.subscribe(new CompletableObserver() /* NFI */ {

            @Override
            public void onSubscribe(Disposable d) {
                try {
                    b[0] = d.isDisposed();

                    d.dispose();

                    b[1] = d.isDisposed();

                    d.dispose();
                } finally {
                    cdl.countDown();
                }
            }

            @Override
            public void onError(Throwable e) {
                // ignored
            }

            @Override
            public void onComplete() {
                // ignored
            }
        });

        try {
            assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
        } catch (InterruptedException ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        }

        assertEquals(false, b[0], "Reports disposed upfront?");
        assertEquals(true, b[1], "Didn't report disposed after?");
    }

    /**
     * Consumer for all base reactive types.
     */
    enum NoOpConsumer implements FlowableSubscriber<Object>, Observer<Object>, MaybeObserver<Object>, SingleObserver<Object>, CompletableObserver {
        INSTANCE;

        @Override
        public void onSubscribe(Disposable d) {
            // deliberately no-op
        }

        @Override
        public void onSuccess(Object value) {
            // deliberately no-op
        }

        @Override
        public void onError(Throwable e) {
            // deliberately no-op
        }

        @Override
        public void onComplete() {
            // deliberately no-op
        }

        @Override
        public void onSubscribe(Subscription s) {
            // deliberately no-op
        }

        @Override
        public void onNext(Object t) {
            // deliberately no-op
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param transform the transform to drive an operator
     */
    public static <T, R> void checkDoubleOnSubscribeMaybe(Function<Maybe<T>, ? extends MaybeSource<R>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Maybe<T>() /* NFI */ {
                @Override
                protected void subscribeActual(MaybeObserver<? super T> observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            MaybeSource<R> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param transform the transform to drive an operator
     */
    public static <T, R> void checkDoubleOnSubscribeMaybeToSingle(Function<Maybe<T>, ? extends SingleSource<R>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Maybe<T>() /* NFI */ {
                @Override
                protected void subscribeActual(MaybeObserver<? super T> observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            SingleSource<R> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param transform the transform to drive an operator
     */
    public static <T, R> void checkDoubleOnSubscribeMaybeToObservable(Function<Maybe<T>, ? extends ObservableSource<R>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Maybe<T>() /* NFI */ {
                @Override
                protected void subscribeActual(MaybeObserver<? super T> observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            ObservableSource<R> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param transform the transform to drive an operator
     */
    public static <T, R> void checkDoubleOnSubscribeMaybeToFlowable(Function<Maybe<T>, ? extends Publisher<R>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Maybe<T>() /* NFI */ {
                @Override
                protected void subscribeActual(MaybeObserver<? super T> observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            Publisher<R> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param transform the transform to drive an operator
     */
    public static <T, R> void checkDoubleOnSubscribeSingleToMaybe(Function<Single<T>, ? extends MaybeSource<R>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Single<T>() /* NFI */ {
                @Override
                protected void subscribeActual(SingleObserver<? super T> observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            MaybeSource<R> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param transform the transform to drive an operator
     */
    public static <T, R> void checkDoubleOnSubscribeSingleToObservable(Function<Single<T>, ? extends ObservableSource<R>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Single<T>() /* NFI */ {
                @Override
                protected void subscribeActual(SingleObserver<? super T> observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            ObservableSource<R> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param transform the transform to drive an operator
     */
    public static <T, R> void checkDoubleOnSubscribeSingleToFlowable(Function<Single<T>, ? extends Publisher<R>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Single<T>() /* NFI */ {
                @Override
                protected void subscribeActual(SingleObserver<? super T> observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            Publisher<R> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param transform the transform to drive an operator
     */
    public static <T> void checkDoubleOnSubscribeMaybeToCompletable(Function<Maybe<T>, ? extends CompletableSource> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Maybe<T>() /* NFI */ {
                @Override
                protected void subscribeActual(MaybeObserver<? super T> observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            CompletableSource out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param transform the transform to drive an operator
     */
    public static <T, R> void checkDoubleOnSubscribeSingle(Function<Single<T>, ? extends SingleSource<R>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Single<T>() /* NFI */ {
                @Override
                protected void subscribeActual(SingleObserver<? super T> observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            SingleSource<R> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param transform the transform to drive an operator
     */
    public static <T, R> void checkDoubleOnSubscribeFlowable(Function<Flowable<T>, ? extends Publisher<R>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Flowable<T>() /* NFI */ {
                @Override
                protected void subscribeActual(Subscriber<? super T> subscriber) {
                    try {
                        BooleanSubscription bs1 = new BooleanSubscription();

                        subscriber.onSubscribe(bs1);

                        BooleanSubscription bs2 = new BooleanSubscription();

                        subscriber.onSubscribe(bs2);

                        b[0] = bs1.isCancelled();
                        b[1] = bs2.isCancelled();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            Publisher<R> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Subscription already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param transform the transform to drive an operator
     */
    @SuppressWarnings("unchecked")
    public static <T> void checkDoubleOnSubscribeParallel(Function<ParallelFlowable<T>, ? extends ParallelFlowable<?>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null, null, null };
            final CountDownLatch cdl = new CountDownLatch(2);

            var source = new ParallelFlowable<T>() /* NFI */ {
                @Override
                public void subscribe(Subscriber<? super T>[] subscribers) {
                    for (int i = 0; i < subscribers.length; i++) {
                        try {
                            BooleanSubscription bs1 = new BooleanSubscription();

                            subscribers[i].onSubscribe(bs1);

                            BooleanSubscription bs2 = new BooleanSubscription();

                            subscribers[i].onSubscribe(bs2);

                            b[i * 2 + 0] = bs1.isCancelled();
                            b[i * 2 + 1] = bs2.isCancelled();
                        } finally {
                            cdl.countDown();
                        }
                    }
                }

                @Override
                public int parallelism() {
                    return 2;
                }
            };

            ParallelFlowable<?> out = transform.apply(source);

            out.subscribe(new Subscriber[] { NoOpConsumer.INSTANCE, NoOpConsumer.INSTANCE });

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "Rail 1 First disposed?");
            assertEquals(true, b[1], "Rail 1 Second not disposed?");

            assertEquals(false, b[2], "Rail 2 First disposed?");
            assertEquals(true, b[3], "Rail 2 Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Subscription already set!");
            assertError(errors, 1, IllegalStateException.class, "Subscription already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }
    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param transform the transform to drive an operator
     */
    public static <T> void checkDoubleOnSubscribeParallelToFlowable(Function<ParallelFlowable<T>, ? extends Flowable<?>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null, null, null };
            final CountDownLatch cdl = new CountDownLatch(2);

            var source = new ParallelFlowable<T>() /* NFI */ {
                @Override
                public void subscribe(Subscriber<? super T>[] subscribers) {
                    for (int i = 0; i < subscribers.length; i++) {
                        try {
                            BooleanSubscription bs1 = new BooleanSubscription();

                            subscribers[i].onSubscribe(bs1);

                            BooleanSubscription bs2 = new BooleanSubscription();

                            subscribers[i].onSubscribe(bs2);

                            b[i * 2 + 0] = bs1.isCancelled();
                            b[i * 2 + 1] = bs2.isCancelled();
                        } finally {
                            cdl.countDown();
                        }
                    }
                }

                @Override
                public int parallelism() {
                    return 2;
                }
            };

            Flowable<?> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "Rail 1 First disposed?");
            assertEquals(true, b[1], "Rail 1 Second not disposed?");

            assertEquals(false, b[2], "Rail 2 First disposed?");
            assertEquals(true, b[3], "Rail 2 Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Subscription already set!");
            assertError(errors, 1, IllegalStateException.class, "Subscription already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param transform the transform to drive an operator
     */
    public static <T, R> void checkDoubleOnSubscribeObservable(Function<Observable<T>, ? extends ObservableSource<R>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Observable<T>() /* NFI */ {
                @Override
                protected void subscribeActual(Observer<? super T> observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            ObservableSource<R> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param transform the transform to drive an operator
     */
    public static <T, R> void checkDoubleOnSubscribeObservableToSingle(Function<Observable<T>, ? extends SingleSource<R>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Observable<T>() /* NFI */ {
                @Override
                protected void subscribeActual(Observer<? super T> observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            SingleSource<R> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param transform the transform to drive an operator
     */
    public static <T, R> void checkDoubleOnSubscribeObservableToMaybe(Function<Observable<T>, ? extends MaybeSource<R>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Observable<T>() /* NFI */ {
                @Override
                protected void subscribeActual(Observer<? super T> observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            MaybeSource<R> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param transform the transform to drive an operator
     */
    public static <T> void checkDoubleOnSubscribeObservableToCompletable(Function<Observable<T>, ? extends CompletableSource> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Observable<T>() /* NFI */ {
                @Override
                protected void subscribeActual(Observer<? super T> observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            CompletableSource out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param transform the transform to drive an operator
     */
    public static <T, R> void checkDoubleOnSubscribeFlowableToObservable(Function<Flowable<T>, ? extends ObservableSource<R>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Flowable<T>() /* NFI */ {
                @Override
                protected void subscribeActual(Subscriber<? super T> subscriber) {
                    try {
                        BooleanSubscription bs1 = new BooleanSubscription();

                        subscriber.onSubscribe(bs1);

                        BooleanSubscription bs2 = new BooleanSubscription();

                        subscriber.onSubscribe(bs2);

                        b[0] = bs1.isCancelled();
                        b[1] = bs2.isCancelled();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            ObservableSource<R> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First cancelled?");
            assertEquals(true, b[1], "Second not cancelled?");

            assertError(errors, 0, IllegalStateException.class, "Subscription already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param transform the transform to drive an operator
     */
    public static <T, R> void checkDoubleOnSubscribeFlowableToSingle(Function<Flowable<T>, ? extends SingleSource<R>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Flowable<T>() /* NFI */ {
                @Override
                protected void subscribeActual(Subscriber<? super T> subscriber) {
                    try {
                        BooleanSubscription bs1 = new BooleanSubscription();

                        subscriber.onSubscribe(bs1);

                        BooleanSubscription bs2 = new BooleanSubscription();

                        subscriber.onSubscribe(bs2);

                        b[0] = bs1.isCancelled();
                        b[1] = bs2.isCancelled();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            SingleSource<R> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First cancelled?");
            assertEquals(true, b[1], "Second not cancelled?");

            assertError(errors, 0, IllegalStateException.class, "Subscription already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param <R> the output value type
     * @param transform the transform to drive an operator
     */
    public static <T, R> void checkDoubleOnSubscribeFlowableToMaybe(Function<Flowable<T>, ? extends MaybeSource<R>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Flowable<T>() /* NFI */ {
                @Override
                protected void subscribeActual(Subscriber<? super T> subscriber) {
                    try {
                        BooleanSubscription bs1 = new BooleanSubscription();

                        subscriber.onSubscribe(bs1);

                        BooleanSubscription bs2 = new BooleanSubscription();

                        subscriber.onSubscribe(bs2);

                        b[0] = bs1.isCancelled();
                        b[1] = bs2.isCancelled();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            MaybeSource<R> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First cancelled?");
            assertEquals(true, b[1], "Second not cancelled?");

            assertError(errors, 0, IllegalStateException.class, "Subscription already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the input value type
     * @param transform the transform to drive an operator
     */
    public static <T> void checkDoubleOnSubscribeFlowableToCompletable(Function<Flowable<T>, ? extends Completable> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            var source = new Flowable<T>() /* NFI */ {
                @Override
                protected void subscribeActual(Subscriber<? super T> subscriber) {
                    try {
                        BooleanSubscription bs1 = new BooleanSubscription();

                        subscriber.onSubscribe(bs1);

                        BooleanSubscription bs2 = new BooleanSubscription();

                        subscriber.onSubscribe(bs2);

                        b[0] = bs1.isCancelled();
                        b[1] = bs2.isCancelled();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            Completable out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First cancelled?");
            assertEquals(true, b[1], "Second not cancelled?");

            assertError(errors, 0, IllegalStateException.class, "Subscription already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param transform the transform to drive an operator
     */
    public static void checkDoubleOnSubscribeCompletable(Function<Completable, ? extends CompletableSource> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            Completable source = new Completable() /* NFI */ {
                @Override
                protected void subscribeActual(CompletableObserver observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            CompletableSource out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the output value tye
     * @param transform the transform to drive an operator
     */
    public static <T> void checkDoubleOnSubscribeCompletableToMaybe(Function<Completable, ? extends MaybeSource<T>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            Completable source = new Completable() /* NFI */ {
                @Override
                protected void subscribeActual(CompletableObserver observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            MaybeSource<T> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param <T> the output value tye
     * @param transform the transform to drive an operator
     */
    public static <T> void checkDoubleOnSubscribeCompletableToSingle(Function<Completable, ? extends SingleSource<T>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            Completable source = new Completable() /* NFI */ {
                @Override
                protected void subscribeActual(CompletableObserver observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            SingleSource<T> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param transform the transform to drive an operator
     */
    public static void checkDoubleOnSubscribeCompletableToFlowable(Function<Completable, ? extends Publisher<?>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            Completable source = new Completable() /* NFI */ {
                @Override
                protected void subscribeActual(CompletableObserver observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            Publisher<?> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the given transformed reactive type reports multiple onSubscribe calls to
     * RxJavaPlugins.
     * @param transform the transform to drive an operator
     */
    public static void checkDoubleOnSubscribeCompletableToObservable(Function<Completable, ? extends ObservableSource<?>> transform) {
        List<Throwable> errors = trackPluginErrors();
        try {
            final Boolean[] b = { null, null };
            final CountDownLatch cdl = new CountDownLatch(1);

            Completable source = new Completable() /* NFI */ {
                @Override
                protected void subscribeActual(CompletableObserver observer) {
                    try {
                        Disposable d1 = Disposable.empty();

                        observer.onSubscribe(d1);

                        Disposable d2 = Disposable.empty();

                        observer.onSubscribe(d2);

                        b[0] = d1.isDisposed();
                        b[1] = d2.isDisposed();
                    } finally {
                        cdl.countDown();
                    }
                }
            };

            ObservableSource<?> out = transform.apply(source);

            out.subscribe(NoOpConsumer.INSTANCE);

            try {
                assertTrue(cdl.await(5, TimeUnit.SECONDS), "Timed out");
            } catch (InterruptedException ex) {
                throw ExceptionHelper.wrapOrThrow(ex);
            }

            assertEquals(false, b[0], "First disposed?");
            assertEquals(true, b[1], "Second not disposed?");

            assertError(errors, 0, IllegalStateException.class, "Disposable already set!");
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Check if the operator applied to a Maybe source propagates dispose properly.
     * @param <T> the source value type
     * @param <U> the output value type
     * @param composer the function to apply an operator to the provided Maybe source
     */
    public static <T, U> void checkDisposedMaybe(Function<Maybe<T>, ? extends MaybeSource<U>> composer) {
        PublishProcessor<T> pp = PublishProcessor.create();

        TestSubscriber<U> ts = new TestSubscriber<>();

        try {
            new MaybeToFlowable<>(composer.apply(pp.singleElement())).subscribe(ts);
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        }

        assertTrue(pp.hasSubscribers(), "Not subscribed to source!");

        ts.cancel();

        assertFalse(pp.hasSubscribers(), "Dispose not propagated!");
    }

    /**
     * Check if the operator applied to a Completable source propagates dispose properly.
     * @param composer the function to apply an operator to the provided Completable source
     */
    public static void checkDisposedCompletable(Function<Completable, ? extends CompletableSource> composer) {
        PublishProcessor<Integer> pp = PublishProcessor.create();

        TestSubscriber<Integer> ts = new TestSubscriber<>();

        try {
            new CompletableToFlowable<Integer>(composer.apply(pp.ignoreElements())).subscribe(ts);
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        }

        assertTrue(pp.hasSubscribers(), "Not subscribed to source!");

        ts.cancel();

        assertFalse(pp.hasSubscribers(), "Dispose not propagated!");
    }

    /**
     * Check if the operator applied to a Maybe source propagates dispose properly.
     * @param <T> the source value type
     * @param <U> the output value type
     * @param composer the function to apply an operator to the provided Maybe source
     */
    public static <T, U> void checkDisposedMaybeToSingle(Function<Maybe<T>, ? extends SingleSource<U>> composer) {
        PublishProcessor<T> pp = PublishProcessor.create();

        TestSubscriber<U> ts = new TestSubscriber<>();

        try {
            new SingleToFlowable<>(composer.apply(pp.singleElement())).subscribe(ts);
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        }

        assertTrue(pp.hasSubscribers());

        ts.cancel();

        assertFalse(pp.hasSubscribers());
    }

    /**
     * Check if the operator applied to a Maybe source propagates dispose properly.
     * @param <T> the source value type
     * @param <U> the output value type
     * @param composer the function to apply an operator to the provided Maybe source
     */
    public static <T, U> void checkDisposedSingleToMaybe(Function<Single<T>, ? extends MaybeSource<U>> composer) {
        PublishProcessor<T> pp = PublishProcessor.create();

        TestSubscriber<U> ts = new TestSubscriber<>();

        try {
            new MaybeToFlowable<>(composer.apply(pp.singleOrError())).subscribe(ts);
        } catch (Throwable ex) {
            throw ExceptionHelper.wrapOrThrow(ex);
        }

        assertTrue(pp.hasSubscribers());

        ts.cancel();

        assertFalse(pp.hasSubscribers());
    }

    /**
     * Check if the TestSubscriber has a CompositeException with the specified class
     * of Throwables in the given order.
     * @param ts the TestSubscriber instance
     * @param classes the array of expected Throwables inside the Composite
     */
    @SafeVarargs
    public static void assertCompositeExceptions(TestSubscriberEx<?> ts, Class<? extends Throwable>... classes) {
        ts
        .assertSubscribed()
        .assertError(CompositeException.class)
        .assertNotComplete();

        List<Throwable> list = compositeList(ts.errors().getFirst());

        assertEquals(classes.length, list.size());

        for (int i = 0; i < classes.length; i++) {
            assertError(list, i, classes[i]);
        }
    }

    /**
     * Check if the TestSubscriber has a CompositeException with the specified class
     * of Throwables in the given order.
     * @param ts the TestSubscriber instance
     * @param classesAndMessages the array of subsequent Class and String instances representing the
     * expected Throwable class and the expected error message
     */
    public static void assertCompositeExceptions(TestSubscriberEx<?> ts, Object... classesAndMessages) {
        ts
        .assertSubscribed()
        .assertError(CompositeException.class)
        .assertNotComplete();

        assertCompositeExceptionListOf(ts.errors().getFirst(), classesAndMessages);
    }

    /**
     * Check if the TestSubscriber has a CompositeException with the specified class
     * of Throwables in the given order.
     * @param to the TestSubscriber instance
     * @param classes the array of expected Throwables inside the Composite
     */
    @SafeVarargs
    public static void assertCompositeExceptions(TestObserverEx<?> to, Class<? extends Throwable>... classes) {
        to
        .assertSubscribed()
        .assertError(CompositeException.class)
        .assertNotComplete();

        List<Throwable> list = compositeList(to.errors().getFirst());

        assertEquals(classes.length, list.size());

        for (int i = 0; i < classes.length; i++) {
            assertError(list, i, classes[i]);
        }
    }

    /**
     * Check if the TestSubscriber has a CompositeException with the specified class
     * of Throwables in the given order.
     * @param to the TestSubscriber instance
     * @param classesAndMessages the array of subsequent Class and String instances representing the
     * expected Throwable class and the expected error message
     */
    public static void assertCompositeExceptions(TestObserverEx<?> to, Object... classesAndMessages) {
        to
        .assertSubscribed()
        .assertError(CompositeException.class)
        .assertNotComplete();

        assertCompositeExceptionListOf(to.errors().getFirst(), classesAndMessages);
    }

    @SuppressWarnings("unchecked")
    static void assertCompositeExceptionListOf(Throwable ex, Object... classesAndMessages) {
        List<Throwable> list = compositeList(ex);

        assertEquals(classesAndMessages.length, 2 * list.size());

        for (int i = 0; i < list.size(); i++) {
            assertError(list, i, (Class<Throwable>)classesAndMessages[2 * i], (String)classesAndMessages[2 * i + 1]);
        }
    }

    /**
     * Emit the given values and complete the Processor.
     * @param <T> the value type
     * @param p the target processor
     * @param values the values to emit
     */
    @SafeVarargs
    public static <T> void emit(Processor<T, ?> p, T... values) {
        for (T v : values) {
            p.onNext(v);
        }
        p.onComplete();
    }

    /**
     * Emit the given values and complete the Subject.
     * @param <T> the value type
     * @param p the target subject
     * @param values the values to emit
     */
    @SafeVarargs
    public static <T> void emit(Subject<T> p, T... values) {
        for (T v : values) {
            p.onNext(v);
        }
        p.onComplete();
    }

    /**
     * Checks if the source is fuseable and its isEmpty/clear works properly.
     * @param <T> the value type
     * @param source the source sequence
     */
    public static <T> void checkFusedIsEmptyClear(Observable<T> source) {
        final CountDownLatch cdl = new CountDownLatch(1);

        final Boolean[] state = { null, null, null, null };

        source.subscribe(new Observer<>() /* NFI */ {
            @Override
            public void onSubscribe(Disposable d) {
                try {
                    if (d instanceof QueueDisposable) {
                        @SuppressWarnings("unchecked")
                        QueueDisposable<Object> qd = (QueueDisposable<Object>) d;
                        state[0] = true;

                        int m = qd.requestFusion(QueueFuseable.ANY);

                        if (m != QueueFuseable.NONE) {
                            state[1] = true;

                            state[2] = qd.isEmpty();

                            qd.clear();

                            state[3] = qd.isEmpty();
                        }
                    }
                    cdl.countDown();
                } finally {
                    d.dispose();
                }
            }

            @Override
            public void onNext(T value) {

            }

            @Override
            public void onError(Throwable e) {

            }

            @Override
            public void onComplete() {

            }
        });

        try {
            assertTrue(cdl.await(5, TimeUnit.SECONDS));

            assertTrue(state[0], "Not fuseable");
            assertTrue(state[1], "Fusion rejected");

            assertNotNull(state[2]);
            assertTrue(state[3], "Did not empty");
        } catch (InterruptedException ex) {
            throw new RuntimeException(ex);
        }
    }

    /**
     * Checks if the source is fuseable and its isEmpty/clear works properly.
     * @param <T> the value type
     * @param source the source sequence
     */
    public static <T> void checkFusedIsEmptyClear(Flowable<T> source) {
        final CountDownLatch cdl = new CountDownLatch(1);

        final Boolean[] state = { null, null, null, null };

        source.subscribe(new FlowableSubscriber<>() /* NFI */ {
            @Override
            public void onSubscribe(Subscription s) {
                try {
                    if (s instanceof QueueSubscription) {
                        @SuppressWarnings("unchecked")
                        QueueSubscription<Object> qs = (QueueSubscription<Object>) s;
                        state[0] = true;

                        int m = qs.requestFusion(QueueFuseable.ANY);

                        if (m != QueueFuseable.NONE) {
                            state[1] = true;

                            state[2] = qs.isEmpty();

                            qs.clear();

                            state[3] = qs.isEmpty();
                        }
                    }
                    cdl.countDown();
                } finally {
                    s.cancel();
                }
            }

            @Override
            public void onNext(T value) {

            }

            @Override
            public void onError(Throwable e) {

            }

            @Override
            public void onComplete() {

            }
        });

        try {
            assertTrue(cdl.await(5, TimeUnit.SECONDS));

            assertTrue(state[0], "Not fuseable");
            assertTrue(state[1], "Fusion rejected");

            assertNotNull(state[2]);
            assertTrue(state[3], "Did not empty");
        } catch (InterruptedException ex) {
            throw new RuntimeException(ex);
        }
    }

    /**
     * Returns an expanded error list of the given test consumer.
     * @param to the test consumer instance
     * @return the list
     */
    public static List<Throwable> errorList(TestObserverEx<?> to) {
        return compositeList(to.errors().getFirst());
    }

    /**
     * Returns an expanded error list of the given test consumer.
     * @param ts the test consumer instance
     * @return the list
     */
    public static List<Throwable> errorList(TestSubscriberEx<?> ts) {
        return compositeList(ts.errors().getFirst());
    }

    /**
     * Tests the given mapping of a bad Observable by emitting the good values, then an error/completion and then
     * a bad value followed by a TestException and a completion.
     * @param <T> the value type
     * @param mapper the mapper that receives a bad Observable and returns a reactive base type (detected via reflection).
     * @param error if true, the good value emission is followed by a TestException("error"), if false then onComplete is called
     * @param badValue the bad value to emit if not null
     * @param goodValue the good value to emit before turning bad, if not null
     * @param expected the expected resulting values, null to ignore values received
     */
    public static <T> void checkBadSourceObservable(Function<Observable<T>, Object> mapper,
            final boolean error, final T goodValue, final T badValue, final Object... expected) {
        List<Throwable> errors = trackPluginErrors();
        try {
            var bad = new Observable<T>() /* NFI */ {
                boolean once;
                @Override
                protected void subscribeActual(Observer<? super T> observer) {
                    observer.onSubscribe(Disposable.empty());

                    if (once) {
                        return;
                    }
                    once = true;

                    if (goodValue != null) {
                        observer.onNext(goodValue);
                    }

                    if (error) {
                        observer.onError(new TestException("error"));
                    } else {
                        observer.onComplete();
                    }

                    if (badValue != null) {
                        observer.onNext(badValue);
                    }
                    observer.onError(new TestException("second"));
                    observer.onComplete();
                }
            };

            Object o = mapper.apply(bad);

            if (o instanceof ObservableSource<?> os) {
                TestObserverEx<Object> to = new TestObserverEx<>();

                os.subscribe(to);

                to.awaitDone(5, TimeUnit.SECONDS);

                to.assertSubscribed();

                if (expected != null) {
                    to.assertValues(expected);
                }
                if (error) {
                    to.assertError(TestException.class)
                    .assertErrorMessage("error")
                    .assertNotComplete();
                } else {
                    to.assertNoErrors().assertComplete();
                }
            }

            if (o instanceof Publisher<?> os) {
                TestSubscriberEx<Object> ts = new TestSubscriberEx<>();

                os.subscribe(ts);

                ts.awaitDone(5, TimeUnit.SECONDS);

                ts.assertSubscribed();

                if (expected != null) {
                    ts.assertValues(expected);
                }
                if (error) {
                    ts.assertError(TestException.class)
                    .assertErrorMessage("error")
                    .assertNotComplete();
                } else {
                    ts.assertNoErrors().assertComplete();
                }
            }

            if (o instanceof SingleSource<?> os) {
                TestObserverEx<Object> to = new TestObserverEx<>();

                os.subscribe(to);

                to.awaitDone(5, TimeUnit.SECONDS);

                to.assertSubscribed();

                if (expected != null) {
                    to.assertValues(expected);
                }
                if (error) {
                    to.assertError(TestException.class)
                    .assertErrorMessage("error")
                    .assertNotComplete();
                } else {
                    to.assertNoErrors().assertComplete();
                }
            }

            if (o instanceof MaybeSource<?> os) {
                TestObserverEx<Object> to = new TestObserverEx<>();

                os.subscribe(to);

                to.awaitDone(5, TimeUnit.SECONDS);

                to.assertSubscribed();

                if (expected != null) {
                    to.assertValues(expected);
                }
                if (error) {
                    to.assertError(TestException.class)
                    .assertErrorMessage("error")
                    .assertNotComplete();
                } else {
                    to.assertNoErrors().assertComplete();
                }
            }

            if (o instanceof CompletableSource os) {
                TestObserverEx<Object> to = new TestObserverEx<>();

                os.subscribe(to);

                to.awaitDone(5, TimeUnit.SECONDS);

                to.assertSubscribed();

                if (expected != null) {
                    to.assertValues(expected);
                }
                if (error) {
                    to.assertError(TestException.class)
                    .assertErrorMessage("error")
                    .assertNotComplete();
                } else {
                    to.assertNoErrors().assertComplete();
                }
            }

            assertUndeliverable(errors, 0, TestException.class, "second");
        } catch (AssertionError ex) {
            throw ex;
        } catch (Throwable ex) {
            throw new RuntimeException(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Tests the given mapping of a bad Observable by emitting the good values, then an error/completion and then
     * a bad value followed by a TestException and a completion.
     * @param <T> the value type
     * @param mapper the mapper that receives a bad Observable and returns a reactive base type (detected via reflection).
     * @param error if true, the good value emission is followed by a TestException("error"), if false then onComplete is called
     * @param badValue the bad value to emit if not null
     * @param goodValue the good value to emit before turning bad, if not null
     * @param expected the expected resulting values, null to ignore values received
     */
    public static <T> void checkBadSourceFlowable(Function<Flowable<T>, Object> mapper,
            final boolean error, final T goodValue, final T badValue, final Object... expected) {
        List<Throwable> errors = trackPluginErrors();
        try {
            var bad = new Flowable<T>() /* NFI */ {
                @Override
                protected void subscribeActual(Subscriber<? super T> subscriber) {
                    subscriber.onSubscribe(new BooleanSubscription());

                    if (goodValue != null) {
                        subscriber.onNext(goodValue);
                    }

                    if (error) {
                        subscriber.onError(new TestException("error"));
                    } else {
                        subscriber.onComplete();
                    }

                    if (badValue != null) {
                        subscriber.onNext(badValue);
                    }
                    subscriber.onError(new TestException("second"));
                    subscriber.onComplete();
                }
            };

            Object o = mapper.apply(bad);

            if (o instanceof ObservableSource<?> os) {
                TestObserverEx<Object> to = new TestObserverEx<>();

                os.subscribe(to);

                to.awaitDone(5, TimeUnit.SECONDS);

                to.assertSubscribed();

                if (expected != null) {
                    to.assertValues(expected);
                }
                if (error) {
                    to.assertError(TestException.class)
                    .assertErrorMessage("error")
                    .assertNotComplete();
                } else {
                    to.assertNoErrors().assertComplete();
                }
            }

            if (o instanceof Publisher<?> os) {
                TestSubscriberEx<Object> ts = new TestSubscriberEx<>();

                os.subscribe(ts);

                ts.awaitDone(5, TimeUnit.SECONDS);

                ts.assertSubscribed();

                if (expected != null) {
                    ts.assertValues(expected);
                }
                if (error) {
                    ts.assertError(TestException.class)
                    .assertErrorMessage("error")
                    .assertNotComplete();
                } else {
                    ts.assertNoErrors().assertComplete();
                }
            }

            if (o instanceof SingleSource<?> os) {
                TestObserverEx<Object> to = new TestObserverEx<>();

                os.subscribe(to);

                to.awaitDone(5, TimeUnit.SECONDS);

                to.assertSubscribed();

                if (expected != null) {
                    to.assertValues(expected);
                }
                if (error) {
                    to.assertError(TestException.class)
                    .assertErrorMessage("error")
                    .assertNotComplete();
                } else {
                    to.assertNoErrors().assertComplete();
                }
            }

            if (o instanceof MaybeSource<?> os) {
                TestObserverEx<Object> to = new TestObserverEx<>();

                os.subscribe(to);

                to.awaitDone(5, TimeUnit.SECONDS);

                to.assertSubscribed();

                if (expected != null) {
                    to.assertValues(expected);
                }
                if (error) {
                    to.assertError(TestException.class)
                    .assertErrorMessage("error")
                    .assertNotComplete();
                } else {
                    to.assertNoErrors().assertComplete();
                }
            }

            if (o instanceof CompletableSource os) {
                TestObserverEx<Object> to = new TestObserverEx<>();

                os.subscribe(to);

                to.awaitDone(5, TimeUnit.SECONDS);

                to.assertSubscribed();

                if (expected != null) {
                    to.assertValues(expected);
                }
                if (error) {
                    to.assertError(TestException.class)
                    .assertErrorMessage("error")
                    .assertNotComplete();
                } else {
                    to.assertNoErrors().assertComplete();
                }
            }

            assertUndeliverable(errors, 0, TestException.class, "second");
        } catch (AssertionError ex) {
            throw ex;
        } catch (Throwable ex) {
            throw new RuntimeException(ex);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    public static <T> void checkInvalidParallelSubscribers(ParallelFlowable<T> source) {
        int n = source.parallelism();

        @SuppressWarnings("unchecked")
        TestSubscriber<Object>[] tss = new TestSubscriber[n + 1];
        for (int i = 0; i <= n; i++) {
            tss[i] = new TestSubscriber<>().withTag("" + i);
        }

        source.subscribe(tss);

        for (int i = 0; i <= n; i++) {
            tss[i].assertFailure(IllegalArgumentException.class);
        }
    }

    /**
     * Creates a fuseable Observable that does not emit anything but rejects
     * fusion requests.
     * @param <T> the element type
     * @return the new Observable
     */
    public static <T> Observable<T> rejectObservableFusion() {
        return new Observable<>() /* NFI */ {
            @Override
            protected void subscribeActual(Observer<? super T> observer) {
                observer.onSubscribe(new QueueDisposable<T>() /* NFI */ {

                    @Override
                    public int requestFusion(int mode) {
                        return 0;
                    }

                    @Override
                    public boolean offer(T value) {
                        throw new IllegalStateException();
                    }

                    @Override
                    public boolean offer(T v1, T v2) {
                        throw new IllegalStateException();
                    }

                    @Override
                    public T poll() throws Exception {
                        return null;
                    }

                    @Override
                    public boolean isEmpty() {
                        return true;
                    }

                    @Override
                    public void clear() {
                    }

                    @Override
                    public void dispose() {
                    }

                    @Override
                    public boolean isDisposed() {
                        return false;
                    }
                });
            }
        };
    }

    /**
     * Creates a fuseable Flowable that does not emit anything but rejects
     * fusion requests.
     * @param <T> the element type
     * @return the new Observable
     */
    public static <T> Flowable<T> rejectFlowableFusion() {
        return new Flowable<>() /* NFI */ {
            @Override
            protected void subscribeActual(Subscriber<? super T> subscriber) {
                subscriber.onSubscribe(new QueueSubscription<T>() /* NFI */ {

                    @Override
                    public int requestFusion(int mode) {
                        return 0;
                    }

                    @Override
                    public boolean offer(T value) {
                        throw new IllegalStateException();
                    }

                    @Override
                    public boolean offer(T v1, T v2) {
                        throw new IllegalStateException();
                    }

                    @Override
                    public T poll() throws Exception {
                        return null;
                    }

                    @Override
                    public boolean isEmpty() {
                        return true;
                    }

                    @Override
                    public void clear() {
                    }

                    @Override
                    public void cancel() {
                    }

                    @Override
                    public void request(long n) {
                    }
                });
            }
        };
    }

    static final class FlowableStripBoundary<T> extends Flowable<T> implements FlowableTransformer<T, T> {

        final Flowable<T> source;

        FlowableStripBoundary(Flowable<T> source) {
            this.source = source;
        }

        @Override
        public Flowable<T> apply(Flowable<T> upstream) {
            return new FlowableStripBoundary<>(upstream);
        }

        @Override
        protected void subscribeActual(Subscriber<? super T> s) {
            source.subscribe(new StripBoundarySubscriber<>(s));
        }

        static final class StripBoundarySubscriber<T> implements FlowableSubscriber<T>, QueueSubscription<T> {

            final Subscriber<? super T> downstream;

            Subscription upstream;

            QueueSubscription<T> qs;

            StripBoundarySubscriber(Subscriber<? super T> downstream) {
                this.downstream = downstream;
            }

            @SuppressWarnings("unchecked")
            @Override
            public void onSubscribe(Subscription subscription) {
                this.upstream = subscription;
                if (subscription instanceof QueueSubscription) {
                    qs = (QueueSubscription<T>)subscription;
                }
                downstream.onSubscribe(this);
            }

            @Override
            public void onNext(T t) {
                downstream.onNext(t);
            }

            @Override
            public void onError(Throwable throwable) {
                downstream.onError(throwable);
            }

            @Override
            public void onComplete() {
                downstream.onComplete();
            }

            @Override
            public int requestFusion(int mode) {
                QueueSubscription<T> fs = qs;
                if (fs != null) {
                    return fs.requestFusion(mode & ~BOUNDARY);
                }
                return NONE;
            }

            @Override
            public boolean offer(T value) {
                throw new UnsupportedOperationException("Should not be called");
            }

            @Override
            public boolean offer(T v1, T v2) {
                throw new UnsupportedOperationException("Should not be called");
            }

            @Override
            public T poll() throws Throwable {
                return qs.poll();
            }

            @Override
            public void clear() {
                qs.clear();
            }

            @Override
            public boolean isEmpty() {
                return qs.isEmpty();
            }

            @Override
            public void request(long n) {
                upstream.request(n);
            }

            @Override
            public void cancel() {
                upstream.cancel();
            }
        }
    }

    /**
     * Strips the {@link QueueFuseable#BOUNDARY} mode flag when the downstream calls {@link QueueSubscription#requestFusion(int)}.
     * <p>
     * By default, many operators use {@link QueueFuseable#BOUNDARY} to indicate upstream side effects
     * should not leak over a fused boundary. However, some tests want to verify if {@link QueueSubscription#poll()} crashes
     * are handled correctly and the most convenient way is to crash {@link Flowable#map} that won't fuse with {@code BOUNDARY}
     * flag. This transformer strips this flag and thus allows the function of {@code map} to be executed as part of the
     * {@code poll()} chain.
     * @param <T> the element type of the flow
     * @return the new Transformer instance
     */
    public static <T> FlowableTransformer<T, T> flowableStripBoundary() {
        return new FlowableStripBoundary<>(null);
    }

    static final class ObservableStripBoundary<T> extends Observable<T> implements ObservableTransformer<T, T> {

        final Observable<T> source;

        ObservableStripBoundary(Observable<T> source) {
            this.source = source;
        }

        @Override
        public Observable<T> apply(Observable<T> upstream) {
            return new ObservableStripBoundary<>(upstream);
        }

        @Override
        protected void subscribeActual(Observer<? super T> observer) {
            source.subscribe(new StripBoundaryObserver<>(observer));
        }

        static final class StripBoundaryObserver<T> implements Observer<T>, QueueDisposable<T> {

            final Observer<? super T> downstream;

            Disposable upstream;

            QueueDisposable<T> qd;

            StripBoundaryObserver(Observer<? super T> downstream) {
                this.downstream = downstream;
            }

            @SuppressWarnings("unchecked")
            @Override
            public void onSubscribe(Disposable d) {
                this.upstream = d;
                if (d instanceof QueueDisposable) {
                    qd = (QueueDisposable<T>)d;
                }
                downstream.onSubscribe(this);
            }

            @Override
            public void onNext(T t) {
                downstream.onNext(t);
            }

            @Override
            public void onError(Throwable throwable) {
                downstream.onError(throwable);
            }

            @Override
            public void onComplete() {
                downstream.onComplete();
            }

            @Override
            public int requestFusion(int mode) {
                QueueDisposable<T> fs = qd;
                if (fs != null) {
                    return fs.requestFusion(mode & ~BOUNDARY);
                }
                return NONE;
            }

            @Override
            public boolean offer(T value) {
                throw new UnsupportedOperationException("Should not be called");
            }

            @Override
            public boolean offer(T v1, T v2) {
                throw new UnsupportedOperationException("Should not be called");
            }

            @Override
            public T poll() throws Throwable {
                return qd.poll();
            }

            @Override
            public void clear() {
                qd.clear();
            }

            @Override
            public boolean isEmpty() {
                return qd.isEmpty();
            }

            @Override
            public void dispose() {
                upstream.dispose();
            }

            @Override
            public boolean isDisposed() {
                return upstream.isDisposed();
            }
        }
    }

    /**
     * Strips the {@link QueueFuseable#BOUNDARY} mode flag when the downstream calls {@link QueueDisposable#requestFusion(int)}.
     * <p>
     * By default, many operators use {@link QueueFuseable#BOUNDARY} to indicate upstream side effects
     * should not leak over a fused boundary. However, some tests want to verify if {@link QueueDisposable#poll()} crashes
     * are handled correctly and the most convenient way is to crash {@link Observable#map} that won't fuse with {@code BOUNDARY}
     * flag. This transformer strips this flag and thus allows the function of {@code map} to be executed as part of the
     * {@code poll()} chain.
     * @param <T> the element type of the flow
     * @return the new Transformer instance
     */
    public static <T> ObservableTransformer<T, T> observableStripBoundary() {
        return new ObservableStripBoundary<>(null);
    }

    public static <T> TestConsumerExConverters<T> testConsumer() {
        return new TestConsumerExConverters<>(false, 0);
    }

    public static <T> TestConsumerExConverters<T> testConsumer(boolean cancelled) {
        return new TestConsumerExConverters<>(cancelled, 0);
    }

    public static <T> TestConsumerExConverters<T> testConsumer(final int fusionMode, final boolean cancelled) {
        return new TestConsumerExConverters<>(cancelled, fusionMode);
    }

    public static <T> TestConsumerExConverters<T> testConsumer(final boolean cancelled, final int fusionMode) {
        return new TestConsumerExConverters<>(cancelled, fusionMode);
    }

    public static <T> FlowableConverter<T, TestSubscriberEx<T>> testSubscriber(final long initialRequest) {
        return testSubscriber(initialRequest, false, 0);
    }

    public static <T> FlowableConverter<T, TestSubscriberEx<T>> testSubscriber(final long initialRequest, final boolean cancelled) {
        return testSubscriber(initialRequest, cancelled, 0);
    }

    public static <T> FlowableConverter<T, TestSubscriberEx<T>> testSubscriber(final long initialRequest, final int fusionMode, final boolean cancelled) {
        return testSubscriber(initialRequest, cancelled, fusionMode);
    }

    public static <T> FlowableConverter<T, TestSubscriberEx<T>> testSubscriber(final long initialRequest, final boolean cancelled, final int fusionMode) {
        return f -> {
            TestSubscriberEx<T> tse = new TestSubscriberEx<>(initialRequest);
            if (cancelled) {
                tse.cancel();
            }
            tse.setInitialFusionMode(fusionMode);
            return f.subscribeWith(tse);
        };
    }

    public static final class TestConsumerExConverters<T> implements
            ObservableConverter<T, TestObserverEx<T>>,
            SingleConverter<T, TestObserverEx<T>>,
            MaybeConverter<T, TestObserverEx<T>>,
            CompletableConverter<TestObserverEx<Void>>,
            FlowableConverter<T, TestSubscriberEx<T>> {

        final boolean cancelled;

        final int fusionMode;

        TestConsumerExConverters(boolean cancelled, int fusionMode) {
            this.cancelled = cancelled;
            this.fusionMode = fusionMode;
        }

        @Override
        public TestObserverEx<Void> apply(Completable upstream) {
            TestObserverEx<Void> toe = new TestObserverEx<>();
            if (cancelled) {
                toe.dispose();
            }
            toe.setInitialFusionMode(fusionMode);
            return upstream.subscribeWith(toe);
        }

        @Override
        public TestObserverEx<T> apply(Maybe<T> upstream) {
            TestObserverEx<T> toe = new TestObserverEx<>();
            if (cancelled) {
                toe.dispose();
            }
            toe.setInitialFusionMode(fusionMode);
            return upstream.subscribeWith(toe);
        }

        @Override
        public TestObserverEx<T> apply(Single<T> upstream) {
            TestObserverEx<T> toe = new TestObserverEx<>();
            if (cancelled) {
                toe.dispose();
            }
            toe.setInitialFusionMode(fusionMode);
            return upstream.subscribeWith(toe);
        }

        @Override
        public TestObserverEx<T> apply(Observable<T> upstream) {
            TestObserverEx<T> toe = new TestObserverEx<>();
            if (cancelled) {
                toe.dispose();
            }
            toe.setInitialFusionMode(fusionMode);
            return upstream.subscribeWith(toe);
        }

        @Override
        public TestSubscriberEx<T> apply(Flowable<T> upstream) {
            TestSubscriberEx<T> tse = new TestSubscriberEx<>();
            if (cancelled) {
                tse.dispose();
            }
            tse.setInitialFusionMode(fusionMode);
            return upstream.subscribeWith(tse);
        }
    }

    @SafeVarargs
    public static <T> TestSubscriberEx<T> assertValueSet(TestSubscriberEx<T> ts, T... values) {
        Set<T> expectedSet = new HashSet<>(Arrays.asList(values));
        for (T t : ts.values()) {
            if (!expectedSet.contains(t)) {
                throw ts.failWith("Item not in the set: " + BaseTestConsumer.valueAndClass(t));
            }
        }
        return ts;
    }

    @SafeVarargs
    public static <T> TestObserverEx<T> assertValueSet(TestObserverEx<T> to, T... values) {
        Set<T> expectedSet = new HashSet<>(Arrays.asList(values));
        for (T t : to.values()) {
            if (!expectedSet.contains(t)) {
                throw to.failWith("Item not in the set: " + BaseTestConsumer.valueAndClass(t));
            }
        }
        return to;
    }

    /**
     * Given a base reactive type name, try to find its source in the current runtime
     * path and return a file to it or null if not found.
     * @param baseClassName the class name such as {@code Maybe}
     * @return the File pointing to the source
     * @throws Exception on error
     */
    public static File findSource(String baseClassName) throws Exception {
        return findSource(baseClassName, "io.reactivex.rxjava4.core");
    }

    /**
     * Given a base reactive type name, try to find its source in the current runtime
     * path and return a file to it or null if not found.
     * @param baseClassName the class name such as {@code Maybe}
     * @param parentPackage the parent package such as {@code io.reactivex.rxjava4.core}
     * @return the File pointing to the source
     * @throws Exception on error
     */
    public static File findSource(String baseClassName, String parentPackage) throws Exception {
        URL u = TestHelper.class.getResource(TestHelper.class.getSimpleName() + ".class");

        String path = new File(u.toURI()).toString().replace('\\', '/');

        parentPackage = parentPackage.replace(".", "/");
//        System.out.println(path);

        // Locate the src/main/java directory
        String p = null;
        while (true) {
            int idx = path.lastIndexOf("/");
            if (idx < 0) {
                break;
            }
            path = path.substring(0, idx);
            String check = path + "/src/main/java";

            if (new File(check).exists()) {
                p = check + "/" + parentPackage + "/" + baseClassName + ".java";
                break;
            }
        }

        if (p == null) {
            System.err.println("Unable to locate the RxJava sources");
            return null;
        }

        File f = new File(p);

        if (f.canRead()) {
            return f;
        }

        new Exception("Can't read " + p).printStackTrace(System.out);
        return null;
    }

    /**
     * Cancels a flow before notifying a transformation and checks if an undeliverable exception
     * has been signaled due to the cancellation.
     * @param transform the operator to test
     * @param <T> the output type of the transformation
     */
    public static <T> void checkUndeliverableUponCancel(FlowableConverter<Integer, T> transform) {
        List<Throwable> errors = TestHelper.trackPluginErrors();
        try {

            final SerialDisposable disposable = new SerialDisposable();

            T result = Flowable.just(1)
            .map((Function<Integer, Integer>) _ -> {
                disposable.dispose();
                throw new TestException();
            })
            .to(transform);

            switch (result) {
                case MaybeSource<?> maybeSource -> {
                    TestObserverEx<Object> to = new TestObserverEx<>();
                    disposable.set(to.asDisposable());

                    maybeSource
                            .subscribe(to);
                    to.assertEmpty();
                }
                case SingleSource<?> singleSource -> {
                    TestObserverEx<Object> to = new TestObserverEx<>();
                    disposable.set(to.asDisposable());

                    singleSource
                            .subscribe(to);
                    to.assertEmpty();
                }
                case CompletableSource completableSource -> {
                    TestObserverEx<Object> to = new TestObserverEx<>();
                    disposable.set(to.asDisposable());

                    completableSource
                            .subscribe(to);
                    to.assertEmpty();
                }
                case ObservableSource<?> observableSource -> {
                    TestObserverEx<Object> to = new TestObserverEx<>();
                    disposable.set(to.asDisposable());

                    observableSource
                            .subscribe(to);
                    to.assertEmpty();
                }
                case Publisher<?> publisher -> {
                    TestSubscriberEx<Object> ts = new TestSubscriberEx<>();
                    disposable.set(Disposable.fromSubscription(ts));

                    publisher
                            .subscribe(ts);
                    ts.assertEmpty();
                }
                default ->
                        fail("Unsupported transformation output: " + result + " of class " + (result != null ? result.getClass() : " <null>"));
            }

            assertFalse(errors.isEmpty(), "No undeliverable errors received");
            TestHelper.assertUndeliverable(errors, 0, TestException.class);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Cancels a flow before notifying a transformation and checks if an undeliverable exception
     * has been signaled due to the cancellation.
     * @param transform the operator to test
     * @param <T> the output type of the transformation
     */
    public static <T> void checkUndeliverableUponCancel(ObservableConverter<Integer, T> transform) {
        List<Throwable> errors = TestHelper.trackPluginErrors();
        try {

            final SerialDisposable disposable = new SerialDisposable();

            T result = Observable.just(1)
            .map((Function<Integer, Integer>) _ -> {
                disposable.dispose();
                throw new TestException();
            })
            .to(transform);

            switch (result) {
                case MaybeSource<?> maybeSource -> {
                    TestObserverEx<Object> to = new TestObserverEx<>();
                    disposable.set(to.asDisposable());

                    maybeSource
                            .subscribe(to);
                    to.assertEmpty();
                }
                case SingleSource<?> singleSource -> {
                    TestObserverEx<Object> to = new TestObserverEx<>();
                    disposable.set(to.asDisposable());

                    singleSource
                            .subscribe(to);
                    to.assertEmpty();
                }
                case CompletableSource completableSource -> {
                    TestObserverEx<Object> to = new TestObserverEx<>();
                    disposable.set(to.asDisposable());

                    completableSource
                            .subscribe(to);
                    to.assertEmpty();
                }
                case ObservableSource<?> observableSource -> {
                    TestObserverEx<Object> to = new TestObserverEx<>();
                    disposable.set(to.asDisposable());

                    observableSource
                            .subscribe(to);
                    to.assertEmpty();
                }
                case Publisher<?> publisher -> {
                    TestSubscriberEx<Object> ts = new TestSubscriberEx<>();
                    disposable.set(Disposable.fromSubscription(ts));

                    publisher
                            .subscribe(ts);
                    ts.assertEmpty();
                }
                default ->
                        fail("Unsupported transformation output: " + result + " of class " + (result != null ? result.getClass() : " <null>"));
            }

            assertFalse(errors.isEmpty(), "No undeliverable errors received");
            TestHelper.assertUndeliverable(errors, 0, TestException.class);
        } finally {
            RxJavaPlugins.reset();
        }
    }

    /**
     * Repeatedly calls System.gc() and sleeps until the current memory usage
     * is less than the given expected usage or the given number of wait loop/time
     * has passed.
     * @param oneSleep how many milliseconds to sleep after a GC.
     * @param maxLoop the maximum number of GC/sleep calls.
     * @param expectedMemoryUsage the memory usage in bytes at max
     * @return the actual memory usage after the loop
     * @throws InterruptedException if the sleep is interrupted
     */
    public static long awaitGC(long oneSleep, int maxLoop, long expectedMemoryUsage) throws InterruptedException {
        MemoryMXBean bean = ManagementFactory.getMemoryMXBean();

        System.gc();

        int i = maxLoop;
        while (i-- != 0) {
            long usage = bean.getHeapMemoryUsage().getUsed();
            if (usage <= expectedMemoryUsage) {
                return usage;
            }
            System.gc();
            Thread.sleep(oneSleep);
        }
        return bean.getHeapMemoryUsage().getUsed();
    }

    /**
     * Assert if the given CompletableFuture fails with a specified error inside an ExecutionException.
     * @param cf the CompletableFuture to test
     * @param error the error class expected
     */
    public static void assertError(CompletableFuture<?> cf, Class<? extends Throwable> error) {
        try {
            cf.get();
            fail("Should have thrown!");
        } catch (Throwable ex) {
            if (!error.isInstance(ex.getCause())) {
                ex.printStackTrace();
                fail("Wrong cause: " + ex.getCause());
            }
        }
    }

    /**
     * Syncs the execution of the given runnable with the execution of the
     * current thread.
     * @param run the other task to run in sync with the current thread
     * @param resume the latch to count down after the {@code run}
     */
    public static void raceOther(Runnable run, CountDownLatch resume) {
        AtomicInteger sync = new AtomicInteger(2);

        Schedulers.single().scheduleDirect(() -> {
            if (sync.decrementAndGet() != 0) {
                while (sync.get() != 0) { }
            }

            run.run();

            resume.countDown();
        });

        if (sync.decrementAndGet() != 0) {
            while (sync.get() != 0) { }
        }
    }

    /**
     * Inserts a ConditionalSubscriber into the chain to trigger the conditional paths
     * without interfering with the requestFusion parts.
     * @param <T> the element type
     * @return the new FlowableTransformer instance
     */
    public static <T> FlowableTransformer<T, T> conditional() {
        return f -> new Flowable<>() /* NFI */ {
            @Override
            protected void subscribeActual(@NonNull Subscriber<@NonNull ? super T> subscriber) {
                f.subscribe(new ForwardingConditionalSubscriber<>(subscriber));
            }
        };
    }

    /**
     * Checks if tasks can be immediately executed on the computation scheduler.
     * @throws ObstructionException if the schedulers don't respond within 1 second
     * @since 4.0.0
     */
    public static void checkObstruction() {
        final int ncpu = Runtime.getRuntime().availableProcessors();

        final CountDownLatch cdl = new CountDownLatch(ncpu);
        final List<Scheduler.Worker> workers = new ArrayList<>();
        final Runnable task = cdl::countDown;

        for (int i = 0; i < ncpu; i++) {
            workers.add(Schedulers.computation().createWorker());
        }
        for (Scheduler.Worker w : workers) {
            w.schedule(task);
        }
        try {
            if (!cdl.await(5, TimeUnit.SECONDS)) {
                int cnt = 0;
                var sb = new StringBuilder();
                for (var e : Thread.getAllStackTraces().entrySet()) {
                    if (e.getKey().getName().contains("Computation")) {
                        cnt++;
                        sb.append("Thread: ").append(e.getKey()).append("\r\n");
                        for (var entry : e.getValue()) {
                            sb.append(" at ").append(entry).append("\r\n");
                        }
                    }
                }

                var ex = new ObstructionException("Obstruction/Timeout detected! ncpu = " + ncpu + ", computation workers = " + cnt + "\r\n" + sb);

                throw ex;
            }
        } catch (InterruptedException ex) {
            throw new ObstructionException("Interrupted: " + ex);
        } finally {
            for (Scheduler.Worker w : workers) {
                w.dispose();
            }
        }
    }
    /**
     * Exception thrown if obstruction was detected.
     */
    public static final class ObstructionException extends RuntimeException {
        @Serial
        private static final long serialVersionUID = -6380717994471291795L;
        public ObstructionException(String message) {
            super(message);
        }
    }

    /**
     * Wraps a Subscriber and exposes it as a fuseable conditional subscriber without interfering with
     * requestFusion.
     * @param <T> the element type
     */
    static final class ForwardingConditionalSubscriber<T> extends BasicQueueSubscription<T> implements ConditionalSubscriber<T> {

        @Serial
        private static final long serialVersionUID = 365317603608134078L;

        final Subscriber<? super T> downstream;

        Subscription upstream;

        QueueSubscription<T> qs;

        ForwardingConditionalSubscriber(Subscriber<? super T> downstream) {
            this.downstream = downstream;
        }

        @SuppressWarnings("unchecked")
        @Override
        public void onSubscribe(@NonNull Subscription s) {
            this.upstream = s;
            if (s instanceof QueueSubscription) {
                this.qs = (QueueSubscription<T>)s;
            }
            downstream.onSubscribe(this);
        }

        @Override
        public void onNext(@NonNull T t) {
            downstream.onNext(t);
        }

        @Override
        public boolean tryOnNext(@NonNull T t) {
            downstream.onNext(t);
            return true;
        }

        @Override
        public void onError(Throwable t) {
            downstream.onError(t);
        }

        @Override
        public void onComplete() {
            downstream.onComplete();
        }

        @Override
        public int requestFusion(int mode) {
            return qs != null ? qs.requestFusion(mode) : 0;
        }

        @Override
        public @Nullable T poll() throws Throwable {
            return qs.poll();
        }

        @Override
        public boolean isEmpty() {
            return qs.isEmpty();
        }

        @Override
        public void clear() {
            qs.clear();
        }

        @Override
        public void request(long n) {
            upstream.request(n);
        }

        @Override
        public void cancel() {
            upstream.cancel();
        }
    }
}