001/* 002 * Copyright (C) 2007 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * http://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package com.google.common.testing; 018 019import static com.google.common.base.Preconditions.checkNotNull; 020import static junit.framework.Assert.assertEquals; 021import static junit.framework.Assert.assertTrue; 022 023import com.google.common.annotations.GwtCompatible; 024import com.google.common.base.Equivalence; 025import com.google.common.collect.ImmutableList; 026import com.google.common.collect.Iterables; 027import com.google.common.collect.Lists; 028import java.util.List; 029 030/** 031 * Tester for equals() and hashCode() methods of a class. 032 * 033 * <p>The simplest use case is: 034 * 035 * <pre> 036 * new EqualsTester().addEqualityGroup(foo).testEquals(); 037 * </pre> 038 * 039 * <p>This tests {@code foo.equals(foo)}, {@code foo.equals(null)}, and a few other operations. 040 * 041 * <p>For more extensive testing, add multiple equality groups. Each group should contain objects 042 * that are equal to each other but unequal to the objects in any other group. For example: 043 * 044 * <pre> 045 * new EqualsTester() 046 * .addEqualityGroup(new User("page"), new User("page")) 047 * .addEqualityGroup(new User("sergey")) 048 * .testEquals(); 049 * </pre> 050 * 051 * <p>This tests: 052 * 053 * <ul> 054 * <li>comparing each object against itself returns true 055 * <li>comparing each object against null returns false 056 * <li>comparing each object against an instance of an incompatible class returns false 057 * <li>comparing each pair of objects within the same equality group returns true 058 * <li>comparing each pair of objects from different equality groups returns false 059 * <li>the hash codes of any two equal objects are equal 060 * </ul> 061 * 062 * <p>When a test fails, the error message labels the objects involved in the failed comparison as 063 * follows: 064 * 065 * <ul> 066 * <li>"{@code [group }<i>i</i>{@code , item }<i>j</i>{@code ]}" refers to the 067 * <i>j</i><sup>th</sup> item in the <i>i</i><sup>th</sup> equality group, where both equality 068 * groups and the items within equality groups are numbered starting from 1. When either a 069 * constructor argument or an equal object is provided, that becomes group 1. 070 * </ul> 071 * 072 * @author Jim McMaster 073 * @author Jige Yu 074 * @since 10.0 075 */ 076@GwtCompatible 077public final class EqualsTester { 078 private static final int REPETITIONS = 3; 079 080 private final List<List<Object>> equalityGroups = Lists.newArrayList(); 081 private final RelationshipTester.ItemReporter itemReporter; 082 083 /** Constructs an empty EqualsTester instance */ 084 public EqualsTester() { 085 this(new RelationshipTester.ItemReporter()); 086 } 087 088 EqualsTester(RelationshipTester.ItemReporter itemReporter) { 089 this.itemReporter = checkNotNull(itemReporter); 090 } 091 092 /** 093 * Adds {@code equalityGroup} with objects that are supposed to be equal to each other and not 094 * equal to any other equality groups added to this tester. 095 */ 096 public EqualsTester addEqualityGroup(Object... equalityGroup) { 097 checkNotNull(equalityGroup); 098 equalityGroups.add(ImmutableList.copyOf(equalityGroup)); 099 return this; 100 } 101 102 /** Run tests on equals method, throwing a failure on an invalid test */ 103 public EqualsTester testEquals() { 104 RelationshipTester<Object> delegate = 105 new RelationshipTester<>( 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( 121 item + " must not be Object#equals to an arbitrary object of another class", 122 !item.equals(NotAnInstance.EQUAL_TO_NOTHING)); 123 assertTrue(item + " must be Object#equals to itself", item.equals(item)); 124 assertEquals( 125 "the Object#hashCode of " + item + " must be consistent", 126 item.hashCode(), 127 item.hashCode()); 128 if (!(item instanceof String)) { 129 assertTrue( 130 item + " must not be Object#equals to its Object#toString representation", 131 !item.equals(item.toString())); 132 } 133 } 134 } 135 136 /** 137 * Class used to test whether equals() correctly handles an instance of an incompatible class. 138 * Since it is a private inner class, the invoker can never pass in an instance to the tester 139 */ 140 private enum NotAnInstance { 141 EQUAL_TO_NOTHING; 142 } 143}