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
30 import java.util.List;
31
32 /**
33 * Tester for equals() and hashCode() methods of a class.
34 *
35 * <p>To use, create a new EqualsTester and add equality groups where each group
36 * contains objects that are supposed to be equal to each other, and objects of
37 * different groups are expected to be unequal. For example:
38 * <pre>
39 * new EqualsTester()
40 * .addEqualityGroup("hello", "h" + "ello")
41 * .addEqualityGroup("world", "wor" + "ld")
42 * .addEqualityGroup(2, 1 + 1)
43 * .testEquals();
44 * </pre>
45 * <p>This tests:
46 * <ul>
47 * <li>comparing each object against itself returns true
48 * <li>comparing each object against null returns false
49 * <li>comparing each object against an instance of an incompatible class
50 * 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 codes 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
74 public final class EqualsTester {
75 private static final int REPETITIONS = 3;
76
77 private final List<List<Object>> equalityGroups = Lists.newArrayList();
78 private final RelationshipTester.ItemReporter itemReporter;
79
80 /**
81 * Constructs an empty EqualsTester instance
82 */
83 public EqualsTester() {
84 this(new RelationshipTester.ItemReporter());
85 }
86
87 EqualsTester(RelationshipTester.ItemReporter itemReporter) {
88 this.itemReporter = checkNotNull(itemReporter);
89 }
90
91 /**
92 * Adds {@code equalityGroup} with objects that are supposed to be equal to
93 * each other and not equal to any other equality groups added to this tester.
94 */
95 public EqualsTester addEqualityGroup(Object... equalityGroup) {
96 checkNotNull(equalityGroup);
97 equalityGroups.add(ImmutableList.copyOf(equalityGroup));
98 return this;
99 }
100
101 /**
102 * Run tests on equals method, throwing a failure on an invalid test
103 */
104 public EqualsTester testEquals() {
105 RelationshipTester<Object> delegate = new RelationshipTester<Object>(
106 Equivalence.equals(), "Object#equals", "Object#hashCode", itemReporter);
107 for (List<Object> group : equalityGroups) {
108 delegate.addRelatedGroup(group);
109 }
110 for (int run = 0; run < REPETITIONS; run++) {
111 testItems();
112 delegate.test();
113 }
114 return this;
115 }
116
117 private void testItems() {
118 for (Object item : Iterables.concat(equalityGroups)) {
119 assertTrue(item + " must not be Object#equals to null", !item.equals(null));
120 assertTrue(item + " must not be Object#equals to an arbitrary object of another class",
121 !item.equals(NotAnInstance.EQUAL_TO_NOTHING));
122 assertEquals(item + " must be Object#equals to itself", item, item);
123 assertEquals("the Object#hashCode of " + item + " must be consistent",
124 item.hashCode(), item.hashCode());
125 }
126 }
127
128 /**
129 * Class used to test whether equals() correctly handles an instance
130 * of an incompatible class. Since it is a private inner class, the
131 * invoker can never pass in an instance to the tester
132 */
133 private enum NotAnInstance {
134 EQUAL_TO_NOTHING;
135 }
136 }