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.GwtCompatible; 24 import com.google.common.base.Equivalence; 25 import com.google.common.collect.Iterables; 26 import com.google.common.collect.Lists; 27 import com.google.errorprone.annotations.CanIgnoreReturnValue; 28 import java.util.ArrayList; 29 import java.util.List; 30 import org.checkerframework.checker.nullness.qual.Nullable; 31 32 /** 33 * Tester for equals() and hashCode() methods of a class. 34 * 35 * <p>The simplest use case is: 36 * 37 * <pre> 38 * new EqualsTester().addEqualityGroup(foo).testEquals(); 39 * </pre> 40 * 41 * <p>This tests {@code foo.equals(foo)}, {@code foo.equals(null)}, and a few other operations. 42 * 43 * <p>For more extensive testing, add multiple equality groups. Each group should contain objects 44 * that are equal to each other but unequal to the objects in any other group. For example: 45 * 46 * <pre> 47 * new EqualsTester() 48 * .addEqualityGroup(new User("page"), new User("page")) 49 * .addEqualityGroup(new User("sergey")) 50 * .testEquals(); 51 * </pre> 52 * 53 * <p>This tests: 54 * 55 * <ul> 56 * <li>comparing each object against itself returns true 57 * <li>comparing each object against null returns false 58 * <li>comparing each object against an instance of an incompatible class returns false 59 * <li>comparing each pair of objects within the same equality group returns true 60 * <li>comparing each pair of objects from different equality groups returns false 61 * <li>the hash codes of any two equal objects are equal 62 * </ul> 63 * 64 * <p>When a test fails, the error message labels the objects involved in the failed comparison as 65 * follows: 66 * 67 * <ul> 68 * <li>"{@code [group }<i>i</i>{@code , item }<i>j</i>{@code ]}" refers to the 69 * <i>j</i><sup>th</sup> item in the <i>i</i><sup>th</sup> equality group, where both equality 70 * groups and the items within equality groups are numbered starting from 1. When either a 71 * constructor argument or an equal object is provided, that becomes group 1. 72 * </ul> 73 * 74 * @author Jim McMaster 75 * @author Jige Yu 76 * @since 10.0 77 */ 78 @GwtCompatible 79 @ElementTypesAreNonnullByDefault 80 public final class EqualsTester { 81 private static final int REPETITIONS = 3; 82 83 private final List<List<Object>> equalityGroups = Lists.newArrayList(); 84 private final RelationshipTester.ItemReporter itemReporter; 85 86 /** Constructs an empty EqualsTester instance */ EqualsTester()87 public EqualsTester() { 88 this(new RelationshipTester.ItemReporter()); 89 } 90 EqualsTester(RelationshipTester.ItemReporter itemReporter)91 EqualsTester(RelationshipTester.ItemReporter itemReporter) { 92 this.itemReporter = checkNotNull(itemReporter); 93 } 94 95 /** 96 * Adds {@code equalityGroup} with objects that are supposed to be equal to each other and not 97 * equal to any other equality groups added to this tester. 98 * 99 * <p>The {@code @Nullable} annotations on the {@code equalityGroup} parameter imply that the 100 * objects, and the array itself, can be null. That is for programmer convenience, when the 101 * objects come from factory methods that are themselves {@code @Nullable}. In reality neither the 102 * array nor its contents can be null, but it is not useful to force the use of {@code 103 * requireNonNull} or the like just to assert that. 104 * 105 * <p>{@code EqualsTester} will always check that every object it is given returns false from 106 * {@code equals(null)}, so it is neither useful nor allowed to include a null value in any 107 * equality group. 108 */ 109 @CanIgnoreReturnValue addEqualityGroup(@ullable Object @ullable .... equalityGroup)110 public EqualsTester addEqualityGroup(@Nullable Object @Nullable ... equalityGroup) { 111 checkNotNull(equalityGroup); 112 List<Object> list = new ArrayList<>(equalityGroup.length); 113 for (int i = 0; i < equalityGroup.length; i++) { 114 Object element = equalityGroup[i]; 115 if (element == null) { 116 throw new NullPointerException("at index " + i); 117 } 118 list.add(element); 119 } 120 equalityGroups.add(list); 121 return this; 122 } 123 124 /** Run tests on equals method, throwing a failure on an invalid test */ 125 @CanIgnoreReturnValue testEquals()126 public EqualsTester testEquals() { 127 RelationshipTester<Object> delegate = 128 new RelationshipTester<>( 129 Equivalence.equals(), "Object#equals", "Object#hashCode", itemReporter); 130 for (List<Object> group : equalityGroups) { 131 delegate.addRelatedGroup(group); 132 } 133 for (int run = 0; run < REPETITIONS; run++) { 134 testItems(); 135 delegate.test(); 136 } 137 return this; 138 } 139 testItems()140 private void testItems() { 141 for (Object item : Iterables.concat(equalityGroups)) { 142 assertTrue(item + " must not be Object#equals to null", !item.equals(null)); 143 assertTrue( 144 item + " must not be Object#equals to an arbitrary object of another class", 145 !item.equals(NotAnInstance.EQUAL_TO_NOTHING)); 146 assertTrue(item + " must be Object#equals to itself", item.equals(item)); 147 assertEquals( 148 "the Object#hashCode of " + item + " must be consistent", 149 item.hashCode(), 150 item.hashCode()); 151 if (!(item instanceof String)) { 152 assertTrue( 153 item + " must not be Object#equals to its Object#toString representation", 154 !item.equals(item.toString())); 155 } 156 } 157 } 158 159 /** 160 * Class used to test whether equals() correctly handles an instance of an incompatible class. 161 * Since it is a private inner class, the invoker can never pass in an instance to the tester 162 */ 163 private enum NotAnInstance { 164 EQUAL_TO_NOTHING; 165 } 166 } 167