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.Beta; 024import com.google.common.annotations.GwtCompatible; 025import com.google.common.base.Equivalence; 026import com.google.common.collect.ImmutableList; 027import com.google.common.collect.Iterables; 028import com.google.common.collect.Lists; 029import java.util.List; 030 031/** 032 * Tester for equals() and hashCode() methods of a class. 033 * 034 * <p>The simplest use case is: 035 * 036 * <pre> 037 * new EqualsTester().addEqualityGroup(foo).testEquals(); 038 * </pre> 039 * 040 * <p>This tests {@code foo.equals(foo)}, {@code foo.equals(null)}, and a few other operations. 041 * 042 * <p>For more extensive testing, add multiple equality groups. Each group should contain objects 043 * that are equal to each other but unequal to the objects in any other group. For example: 044 * 045 * <pre> 046 * new EqualsTester() 047 * .addEqualityGroup(new User("page"), new User("page")) 048 * .addEqualityGroup(new User("sergey")) 049 * .testEquals(); 050 * </pre> 051 * 052 * <p>This tests: 053 * 054 * <ul> 055 * <li>comparing each object against itself returns true 056 * <li>comparing each object against null returns false 057 * <li>comparing each object against an instance of an incompatible class returns false 058 * <li>comparing each pair of objects within the same equality group returns true 059 * <li>comparing each pair of objects from different equality groups returns false 060 * <li>the hash codes of any two equal objects are equal 061 * </ul> 062 * 063 * <p>When a test fails, the error message labels the objects involved in the failed comparison as 064 * follows: 065 * 066 * <ul> 067 * <li>"{@code [group }<i>i</i>{@code , item }<i>j</i>{@code ]}" refers to the 068 * <i>j</i><sup>th</sup> item in the <i>i</i><sup>th</sup> equality group, where both equality 069 * groups and the items within equality groups are numbered starting from 1. When either a 070 * constructor argument or an equal object is provided, that becomes group 1. 071 * </ul> 072 * 073 * @author Jim McMaster 074 * @author Jige Yu 075 * @since 10.0 076 */ 077@Beta 078@GwtCompatible 079public final class EqualsTester { 080 private static final int REPETITIONS = 3; 081 082 private final List<List<Object>> equalityGroups = Lists.newArrayList(); 083 private final RelationshipTester.ItemReporter itemReporter; 084 085 /** Constructs an empty EqualsTester instance */ 086 public EqualsTester() { 087 this(new RelationshipTester.ItemReporter()); 088 } 089 090 EqualsTester(RelationshipTester.ItemReporter itemReporter) { 091 this.itemReporter = checkNotNull(itemReporter); 092 } 093 094 /** 095 * Adds {@code equalityGroup} with objects that are supposed to be equal to each other and not 096 * equal to any other equality groups added to this tester. 097 */ 098 public EqualsTester addEqualityGroup(Object... equalityGroup) { 099 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 } 131 } 132 133 /** 134 * Class used to test whether equals() correctly handles an instance of an incompatible class. 135 * Since it is a private inner class, the invoker can never pass in an instance to the tester 136 */ 137 private enum NotAnInstance { 138 EQUAL_TO_NOTHING; 139 } 140}