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.Equivalence;
26import com.google.common.collect.ImmutableList;
27import com.google.common.collect.Iterables;
28import com.google.common.collect.Lists;
29
30import 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
74public 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}
137