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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.RelationshipAssertion;
     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 Objects#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   EquivalenceTester(final Equivalence<? super T> equivalence) {
     69     this.equivalence = checkNotNull(equivalence);
     70     this.delegate = new RelationshipTester<T>(new RelationshipAssertion<T>() {
     71       @Override public void assertRelated(T item, T related) {
     72         assertTrue("$ITEM must be equivalent to $RELATED", equivalence.equivalent(item, related));
     73         int itemHash = equivalence.hash(item);
     74         int relatedHash = equivalence.hash(related);
     75         assertEquals("the hash (" + itemHash + ") of $ITEM must be equal to the hash ("
     76             + relatedHash + ") of $RELATED", itemHash, relatedHash);
     77       }
     78 
     79       @Override public void assertUnrelated(T item, T unrelated) {
     80         assertTrue("$ITEM must be inequivalent to $UNRELATED",
     81             !equivalence.equivalent(item, unrelated));
     82       }
     83     });
     84   }
     85 
     86   public static <T> EquivalenceTester<T> of(Equivalence<? super T> equivalence) {
     87     return new EquivalenceTester<T>(equivalence);
     88   }
     89 
     90   /**
     91    * Adds a group of objects that are supposed to be equivalent to each other
     92    * and not equivalent to objects in any other equivalence group added to this
     93    * tester.
     94    */
     95   public EquivalenceTester<T> addEquivalenceGroup(T first, T... rest) {
     96     addEquivalenceGroup(Lists.asList(first, rest));
     97     return this;
     98   }
     99 
    100   public EquivalenceTester<T> addEquivalenceGroup(Iterable<T> group) {
    101     delegate.addRelatedGroup(group);
    102     items.addAll(ImmutableList.copyOf(group));
    103     return this;
    104   }
    105 
    106   /** Run tests on equivalence methods, throwing a failure on an invalid test */
    107   public EquivalenceTester<T> test() {
    108     for (int run = 0; run < REPETITIONS; run++) {
    109       testItems();
    110       delegate.test();
    111     }
    112     return this;
    113   }
    114 
    115   private void testItems() {
    116     for (T item : items) {
    117       assertTrue(item + " must be inequivalent to null", !equivalence.equivalent(item, null));
    118       assertTrue("null must be inequivalent to " + item, !equivalence.equivalent(null, item));
    119       assertTrue(item + " must be equivalent to itself", equivalence.equivalent(item, item));
    120       assertEquals("the hash of " + item + " must be consistent", equivalence.hash(item),
    121           equivalence.hash(item));
    122     }
    123   }
    124 }
    125