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
17 package com.google.common.testing;
18
19 import static com.google.common.base.Preconditions.checkNotNull;
20 import static junit.framework.Assert.assertEquals;
21 import static junit.framework.Assert.assertTrue;
22
23 import com.google.common.annotations.Beta;
24 import com.google.common.annotations.GwtCompatible;
25 import com.google.common.base.Equivalence;
26 import com.google.common.collect.ImmutableList;
27 import com.google.common.collect.Iterables;
28 import com.google.common.collect.Lists;
29 import java.util.List;
30
31 /**
32 * Tester for equals() and hashCode() methods of a class.
33 *
34 * <p>The simplest use case is:
35 *
36 * <pre>
37 * new EqualsTester().addEqualityGroup(foo).testEquals();
38 * </pre>
39 *
40 * <p>This tests {@code foo.equals(foo)}, {@code foo.equals(null)}, and a few other operations.
41 *
42 * <p>For more extensive testing, add multiple equality groups. Each group should contain objects
43 * that are equal to each other but unequal to the objects in any other group. For example:
44 *
45 * <pre>
46 * new EqualsTester()
47 * .addEqualityGroup(new User("page"), new User("page"))
48 * .addEqualityGroup(new User("sergey"))
49 * .testEquals();
50 * </pre>
51 *
52 * <p>This tests:
53 *
54 * <ul>
55 * <li>comparing each object against itself returns true
56 * <li>comparing each object against null returns false
57 * <li>comparing each object against an instance of an incompatible class returns false
58 * <li>comparing each pair of objects within the same equality group returns true
59 * <li>comparing each pair of objects from different equality groups returns false
60 * <li>the hash codes of any two equal objects are equal
61 * </ul>
62 *
63 * <p>When a test fails, the error message labels the objects involved in the failed comparison as
64 * follows:
65 *
66 * <ul>
67 * <li>"{@code [group }<i>i</i>{@code , item }<i>j</i>{@code ]}" refers to the
68 * <i>j</i><sup>th</sup> item in the <i>i</i><sup>th</sup> equality group, where both equality
69 * groups and the items within equality groups are numbered starting from 1. When either a
70 * constructor argument or an equal object is provided, that becomes group 1.
71 * </ul>
72 *
73 * @author Jim McMaster
74 * @author Jige Yu
75 * @since 10.0
76 */
77 @Beta
78 @GwtCompatible
79 public final class EqualsTester {
80 private static final int REPETITIONS = 3;
81
82 private final List<List<Object>> equalityGroups = Lists.newArrayList();
83 private final RelationshipTester.ItemReporter itemReporter;
84
85 /** Constructs an empty EqualsTester instance */
86 public EqualsTester() {
87 this(new RelationshipTester.ItemReporter());
88 }
89
90 EqualsTester(RelationshipTester.ItemReporter itemReporter) {
91 this.itemReporter = checkNotNull(itemReporter);
92 }
93
94 /**
95 * Adds {@code equalityGroup} with objects that are supposed to be equal to each other and not
96 * equal to any other equality groups added to this tester.
97 */
98 public EqualsTester addEqualityGroup(Object... equalityGroup) {
99 checkNotNull(equalityGroup);
100 equalityGroups.add(ImmutableList.copyOf(equalityGroup));
101 return this;
102 }
103
104 /** Run tests on equals method, throwing a failure on an invalid test */
105 public EqualsTester testEquals() {
106 RelationshipTester<Object> delegate =
107 new RelationshipTester<>(
108 Equivalence.equals(), "Object#equals", "Object#hashCode", itemReporter);
109 for (List<Object> group : equalityGroups) {
110 delegate.addRelatedGroup(group);
111 }
112 for (int run = 0; run < REPETITIONS; run++) {
113 testItems();
114 delegate.test();
115 }
116 return this;
117 }
118
119 private void testItems() {
120 for (Object item : Iterables.concat(equalityGroups)) {
121 assertTrue(item + " must not be Object#equals to null", !item.equals(null));
122 assertTrue(
123 item + " must not be Object#equals to an arbitrary object of another class",
124 !item.equals(NotAnInstance.EQUAL_TO_NOTHING));
125 assertEquals(item + " must be Object#equals to itself", item, item);
126 assertEquals(
127 "the Object#hashCode of " + item + " must be consistent",
128 item.hashCode(),
129 item.hashCode());
130 if (!(item instanceof String)) {
131 assertTrue(
132 item + " must not be Object#equals to its Object#toString representation",
133 !item.equals(item.toString()));
134 }
135 }
136 }
137
138 /**
139 * Class used to test whether equals() correctly handles an instance of an incompatible class.
140 * Since it is a private inner class, the invoker can never pass in an instance to the tester
141 */
142 private enum NotAnInstance {
143 EQUAL_TO_NOTHING;
144 }
145 }