guava

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/*
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 * Copyright (C) 2011 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.testing;
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import static com.google.common.base.Preconditions.checkNotNull;
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import static junit.framework.Assert.assertEquals;
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import static junit.framework.Assert.assertTrue;
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import com.google.common.annotations.GwtCompatible;
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import com.google.common.base.Equivalence;
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import com.google.common.collect.ImmutableList;
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import com.google.common.collect.Lists;
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import com.google.common.testing.RelationshipTester.ItemReporter;
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import com.google.errorprone.annotations.CanIgnoreReturnValue;
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import java.util.List;
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/**
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 * Tester for {@link Equivalence} relationships between groups of objects.
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 *
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 * <p>To use, create a new {@link EquivalenceTester} and add equivalence groups where each group
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 * contains objects that are supposed to be equal to each other. Objects of different groups are
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 * expected to be unequal. For example:
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 *
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 * <pre>{@code
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 * EquivalenceTester.of(someStringEquivalence)
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 *     .addEquivalenceGroup("hello", "h" + "ello")
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 *     .addEquivalenceGroup("world", "wor" + "ld")
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 *     .test();
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 * }</pre>
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 *
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 * <p>Note that testing {@link Object#equals(Object)} is more simply done using the {@link
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 * EqualsTester}. It includes an extra test against an instance of an arbitrary class without having
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 * to explicitly add another equivalence group.
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 *
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 * @author Gregory Kick
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 * @since 10.0
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 */
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@GwtCompatible
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@ElementTypesAreNonnullByDefault
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public final class EquivalenceTester<T> {
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  private static final int REPETITIONS = 3;
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  private final Equivalence<? super T> equivalence;
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  private final RelationshipTester<T> delegate;
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  private final List<T> items = Lists.newArrayList();
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  private EquivalenceTester(Equivalence<? super T> equivalence) {
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    this.equivalence = checkNotNull(equivalence);
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    this.delegate = new RelationshipTester<>(equivalence, "equivalent", "hash", new ItemReporter());
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  }
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  public static <T> EquivalenceTester<T> of(Equivalence<? super T> equivalence) {
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    return new EquivalenceTester<>(equivalence);
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  }
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  /**
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   * Adds a group of objects that are supposed to be equivalent to each other and not equivalent to
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   * objects in any other equivalence group added to this tester.
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   */
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  @CanIgnoreReturnValue
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  public EquivalenceTester<T> addEquivalenceGroup(T first, T... rest) {
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    addEquivalenceGroup(Lists.asList(first, rest));
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    return this;
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  }
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  @CanIgnoreReturnValue
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  public EquivalenceTester<T> addEquivalenceGroup(Iterable<T> group) {
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    delegate.addRelatedGroup(group);
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    items.addAll(ImmutableList.copyOf(group));
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    return this;
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  }
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  /** Run tests on equivalence methods, throwing a failure on an invalid test */
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  @CanIgnoreReturnValue
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  public EquivalenceTester<T> test() {
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    for (int run = 0; run < REPETITIONS; run++) {
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      testItems();
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      delegate.test();
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    }
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    return this;
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  }
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  private void testItems() {
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    for (T item : items) {
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      /*
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       * TODO(cpovirk): consider no longer running these equivalent() tests on every Equivalence,
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       * since the Equivalence base type now implements this logic itself
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       */
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      assertTrue(item + " must be inequivalent to null", !equivalence.equivalent(item, null));
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      assertTrue("null must be inequivalent to " + item, !equivalence.equivalent(null, item));
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      assertTrue(item + " must be equivalent to itself", equivalence.equivalent(item, item));
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      assertEquals(
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          "the hash of " + item + " must be consistent",
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          equivalence.hash(item),
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          equivalence.hash(item));
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    }
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  }
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}
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