EqualsTester.java revision 1d580d0f6ee4f21eb309ba7b509d2c6d671c4044 
1/*
2 * Copyright (C) 2007 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.testing;
18
19import static com.google.common.base.Preconditions.checkNotNull;
20import static junit.framework.Assert.assertEquals;
21import static junit.framework.Assert.assertTrue;
22
23import com.google.common.annotations.Beta;
24import com.google.common.annotations.GwtCompatible;
25import com.google.common.base.Objects;
26import com.google.common.collect.ImmutableList;
27import com.google.common.collect.Iterables;
28import com.google.common.collect.Lists;
29import com.google.common.testing.RelationshipTester.RelationshipAssertion;
30
31import java.util.List;
32
33/**
34 * Tester for equals() and hashCode() methods of a class.
35 *
36 * <p>To use, create a new EqualsTester and add equality groups where each group
37 * contains objects that are supposed to be equal to each other, and objects of
38 * different groups are expected to be unequal. For example:
39 * <pre>
40 * new EqualsTester()
41 *     .addEqualityGroup("hello", "h" + "ello")
42 *     .addEqualityGroup("world", "wor" + "ld")
43 *     .addEqualityGroup(2, 1 + 1)
44 *     .testEquals();
45 * </pre>
46 * This tests:
47 * <ul>
48 * <li>comparing each object against itself returns true
49 * <li>comparing each object against null returns false
50 * <li>comparing each object an instance of an incompatible class returns false
51 * <li>comparing each pair of objects within the same equality group returns
52 *     true
53 * <li>comparing each pair of objects from different equality groups returns
54 *     false
55 * <li>the hash code of any two equal objects are equal
56 * </ul>
57 *
58 * <p>When a test fails, the error message labels the objects involved in
59 * the failed comparison as follows:
60 * <ul>
61 *   <li>"{@code [group }<i>i</i>{@code , item }<i>j</i>{@code ]}" refers to the
62 *       <i>j</i><sup>th</sup> item in the <i>i</i><sup>th</sup> equality group,
63 *       where both equality groups and the items within equality groups are
64 *       numbered starting from 1.  When either a constructor argument or an
65 *       equal object is provided, that becomes group 1.
66 * </ul>
67 *
68 * @author Jim McMaster
69 * @author Jige Yu
70 * @since 10.0
71 */
72@Beta
73@GwtCompatible
74public final class EqualsTester {
75  private static final int REPETITIONS = 3;
76
77  private final List<List<Object>> equalityGroups = Lists.newArrayList();
78
79  /**
80   * Constructs an empty EqualsTester instance
81   */
82  public EqualsTester() {}
83
84  /**
85   * Adds {@code equalityGroup} with objects that are supposed to be equal to
86   * each other and not equal to any other equality groups added to this tester.
87   */
88  public EqualsTester addEqualityGroup(Object... equalityGroup) {
89    checkNotNull(equalityGroup);
90    equalityGroups.add(ImmutableList.copyOf(equalityGroup));
91    return this;
92  }
93
94  /**
95   * Run tests on equals method, throwing a failure on an invalid test
96   */
97  public EqualsTester testEquals() {
98    RelationshipTester<Object> delegate = new RelationshipTester<Object>(
99        new RelationshipAssertion<Object>() {
100          @Override public void assertRelated(Object item, Object related) {
101            assertEquals("$ITEM must be equal to $RELATED", item, related);
102            int itemHash = item.hashCode();
103            int relatedHash = related.hashCode();
104            assertEquals("the hash (" + itemHash + ") of $ITEM must be equal to the hash ("
105                + relatedHash +") of $RELATED", itemHash, relatedHash);
106          }
107
108          @Override public void assertUnrelated(Object item, Object unrelated) {
109            // TODO(cpovirk): should this implementation (and
110            // RelationshipAssertions in general) accept null inputs?
111            assertTrue("$ITEM must be unequal to $UNRELATED", !Objects.equal(item, unrelated));
112          }
113        });
114    for (List<Object> group : equalityGroups) {
115      delegate.addRelatedGroup(group);
116    }
117    for (int run = 0; run < REPETITIONS; run++) {
118      testItems();
119      delegate.test();
120    }
121    return this;
122  }
123
124  private void testItems() {
125    for (Object item : Iterables.concat(equalityGroups)) {
126      assertTrue(item + " must be unequal to null", !item.equals(null));
127      assertTrue(item + " must be unequal to an arbitrary object of another class",
128          !item.equals(NotAnInstance.EQUAL_TO_NOTHING));
129      assertEquals(item + " must be equal to itself", item, item);
130      assertEquals("the hash of " + item + " must be consistent", item.hashCode(), item.hashCode());
131    }
132  }
133
134  /**
135   * Class used to test whether equals() correctly handles an instance
136   * of an incompatible class.  Since it is a private inner class, the
137   * invoker can never pass in an instance to the tester
138   */
139  private enum NotAnInstance {
140    EQUAL_TO_NOTHING;
141  }
142}
143