guava

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/*
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 * Copyright (C) 2007 The Guava Authors
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 *
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 * Licensed under the Apache License, Version 2.0 (the "License");
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 * you may not use this file except in compliance with the License.
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 * You may obtain a copy of the License at
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 *
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 * http://www.apache.org/licenses/LICENSE-2.0
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 *
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 * Unless required by applicable law or agreed to in writing, software
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 * distributed under the License is distributed on an "AS IS" BASIS,
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 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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 * See the License for the specific language governing permissions and
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 * limitations under the License.
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 */
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package com.google.common.collect.testing;
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import com.google.common.annotations.GwtCompatible;
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import java.util.Collections;
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import java.util.Iterator;
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import org.checkerframework.checker.nullness.qual.Nullable;
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/**
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 * A utility for testing an Iterator implementation by comparing its behavior to that of a "known
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 * good" reference implementation. In order to accomplish this, it's important to test a great
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 * variety of sequences of the {@link Iterator#next}, {@link Iterator#hasNext} and {@link
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 * Iterator#remove} operations. This utility takes the brute-force approach of trying <i>all</i>
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 * possible sequences of these operations, up to a given number of steps. So, if the caller
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 * specifies to use <i>n</i> steps, a total of <i>3^n</i> tests are actually performed.
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 *
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 * <p>For instance, if <i>steps</i> is 5, one example sequence that will be tested is:
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 *
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 * <ol>
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 *   <li>remove();
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 *   <li>hasNext()
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 *   <li>hasNext();
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 *   <li>remove();
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 *   <li>next();
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 * </ol>
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 *
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 * <p>This particular order of operations may be unrealistic, and testing all 3^5 of them may be
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 * thought of as overkill; however, it's difficult to determine which proper subset of this massive
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 * set would be sufficient to expose any possible bug. Brute force is simpler.
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 *
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 * <p>To use this class the concrete subclass must implement the {@link
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 * IteratorTester#newTargetIterator()} method. This is because it's impossible to test an Iterator
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 * without changing its state, so the tester needs a steady supply of fresh Iterators.
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 *
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 * <p>If your iterator supports modification through {@code remove()}, you may wish to override the
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 * verify() method, which is called <em>after</em> each sequence and is guaranteed to be called
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 * using the latest values obtained from {@link IteratorTester#newTargetIterator()}.
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 *
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 * <p>The value you pass to the parameter {@code steps} should be greater than the length of your
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 * iterator, so that this class can check that your iterator behaves correctly when it is exhausted.
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 *
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 * <p>For example, to test {@link java.util.Collections#unmodifiableList(java.util.List)
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 * Collections.unmodifiableList}'s iterator:
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 *
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 * <pre>{@code
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 * List<String> expectedElements =
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 *     Arrays.asList("a", "b", "c", "d", "e");
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 * List<String> actualElements =
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 *     Collections.unmodifiableList(
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 *         Arrays.asList("a", "b", "c", "d", "e"));
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 * IteratorTester<String> iteratorTester =
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 *     new IteratorTester<String>(
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 *         6,
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 *         IteratorFeature.UNMODIFIABLE,
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 *         expectedElements,
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 *         IteratorTester.KnownOrder.KNOWN_ORDER) {
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 *       @Override
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 *       protected Iterator<String> newTargetIterator() {
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 *         return actualElements.iterator();
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 *       }
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 *     };
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 * iteratorTester.test();
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 * iteratorTester.testForEachRemaining();
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 * }</pre>
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 *
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 * <p><b>Note</b>: It is necessary to use {@code IteratorTester.KnownOrder} as shown above, rather
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 * than {@code KnownOrder} directly, because otherwise the code cannot be compiled.
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 *
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 * @author Kevin Bourrillion
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 * @author Chris Povirk
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 */
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@GwtCompatible
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@ElementTypesAreNonnullByDefault
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public abstract class IteratorTester<E extends @Nullable Object>
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    extends AbstractIteratorTester<E, Iterator<E>> {
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  /**
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   * Creates an IteratorTester.
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   *
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   * @param steps how many operations to test for each tested pair of iterators
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   * @param features the features supported by the iterator
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   */
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  protected IteratorTester(
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      int steps,
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      Iterable<? extends IteratorFeature> features,
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      Iterable<E> expectedElements,
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      KnownOrder knownOrder) {
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    super(steps, Collections.<E>singleton(null), features, expectedElements, knownOrder, 0);
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  }
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  @Override
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  protected final Iterable<Stimulus<E, Iterator<E>>> getStimulusValues() {
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    return iteratorStimuli();
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  }
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}
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