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      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 
     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 
     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    */
     83   public EquivalenceTester<T> addEquivalenceGroup(T first, T... rest) {
     84     addEquivalenceGroup(Lists.asList(first, rest));
     85     return this;
     86   }
     87 
     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 */
     95   public EquivalenceTester<T> test() {
     96     for (int run = 0; run < REPETITIONS; run++) {
     97       testItems();
     98       delegate.test();
     99     }
    100     return this;
    101   }
    102 
    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