1 /*
2  * Copyright (C) 2011 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.Lists;
28 import com.google.common.testing.RelationshipTester.ItemReporter;
29 
30 import java.util.List;
31 
32 /**
33  * Tester for {@link Equivalence} relationships between groups of objects.
34  *
35  * <p>
36  * To use, create a new {@link EquivalenceTester} and add equivalence groups
37  * where each group contains objects that are supposed to be equal to each
38  * other. Objects of different groups are expected to be unequal. For example:
39  *
40  * <pre>
41  * {@code
42  * EquivalenceTester.of(someStringEquivalence)
43  *     .addEquivalenceGroup("hello", "h" + "ello")
44  *     .addEquivalenceGroup("world", "wor" + "ld")
45  *     .test();
46  * }
47  * </pre>
48  *
49  * <p>
50  * Note that testing {@link Object#equals(Object)} is more simply done using
51  * the {@link EqualsTester}. It includes an extra test against an instance of an
52  * arbitrary class without having to explicitly add another equivalence group.
53  *
54  * @author Gregory Kick
55  * @since 10.0
56  *
57  * TODO(gak): turn this into a test suite so that each test can fail
58  * independently
59  */
60 @Beta
61 @GwtCompatible public final class EquivalenceTester<T> {
62   private static final int REPETITIONS = 3;
63 
64   private final Equivalence<? super T> equivalence;
65   private final RelationshipTester<T> delegate;
66   private final List<T> items = Lists.newArrayList();
67 
EquivalenceTester(Equivalence<? super T> equivalence)68   private EquivalenceTester(Equivalence<? super T> equivalence) {
69     this.equivalence = checkNotNull(equivalence);
70     this.delegate = new RelationshipTester<T>(
71         equivalence, "equivalent", "hash", new ItemReporter());
72   }
73 
of(Equivalence<? super T> equivalence)74   public static <T> EquivalenceTester<T> of(Equivalence<? super T> equivalence) {
75     return new EquivalenceTester<T>(equivalence);
76   }
77 
78   /**
79    * Adds a group of objects that are supposed to be equivalent to each other
80    * and not equivalent to objects in any other equivalence group added to this
81    * tester.
82    */
addEquivalenceGroup(T first, T... rest)83   public EquivalenceTester<T> addEquivalenceGroup(T first, T... rest) {
84     addEquivalenceGroup(Lists.asList(first, rest));
85     return this;
86   }
87 
addEquivalenceGroup(Iterable<T> group)88   public EquivalenceTester<T> addEquivalenceGroup(Iterable<T> group) {
89     delegate.addRelatedGroup(group);
90     items.addAll(ImmutableList.copyOf(group));
91     return this;
92   }
93 
94   /** Run tests on equivalence methods, throwing a failure on an invalid test */
test()95   public EquivalenceTester<T> test() {
96     for (int run = 0; run < REPETITIONS; run++) {
97       testItems();
98       delegate.test();
99     }
100     return this;
101   }
102 
testItems()103   private void testItems() {
104     for (T item : items) {
105       /*
106        * TODO(cpovirk): consider no longer running these equivalent() tests on every Equivalence,
107        * since the Equivalence base type now implements this logic itself
108        */
109       assertTrue(item + " must be inequivalent to null", !equivalence.equivalent(item, null));
110       assertTrue("null must be inequivalent to " + item, !equivalence.equivalent(null, item));
111       assertTrue(item + " must be equivalent to itself", equivalence.equivalent(item, item));
112       assertEquals("the hash of " + item + " must be consistent", equivalence.hash(item),
113           equivalence.hash(item));
114     }
115   }
116 }
117