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/*
* Copyright (C) 2007 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.common.testing;
import static com.google.common.base.Preconditions.checkNotNull;
import static junit.framework.Assert.assertEquals;
import static junit.framework.Assert.assertTrue;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Objects;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import com.google.common.collect.Lists;
import com.google.common.testing.RelationshipTester.RelationshipAssertion;
import java.util.List;
/**
* Tester for equals() and hashCode() methods of a class.
*
* <p>To use, create a new EqualsTester and add equality groups where each group
* contains objects that are supposed to be equal to each other, and objects of
* different groups are expected to be unequal. For example:
* <pre>
* new EqualsTester()
* .addEqualityGroup("hello", "h" + "ello")
* .addEqualityGroup("world", "wor" + "ld")
* .addEqualityGroup(2, 1 + 1)
* .testEquals();
* </pre>
* This tests:
* <ul>
* <li>comparing each object against itself returns true
* <li>comparing each object against null returns false
* <li>comparing each object an instance of an incompatible class returns false
* <li>comparing each pair of objects within the same equality group returns
* true
* <li>comparing each pair of objects from different equality groups returns
* false
* <li>the hash code of any two equal objects are equal
* </ul>
*
* <p>When a test fails, the error message labels the objects involved in
* the failed comparison as follows:
* <ul>
* <li>"{@code [group }<i>i</i>{@code , item }<i>j</i>{@code ]}" refers to the
* <i>j</i><sup>th</sup> item in the <i>i</i><sup>th</sup> equality group,
* where both equality groups and the items within equality groups are
* numbered starting from 1. When either a constructor argument or an
* equal object is provided, that becomes group 1.
* </ul>
*
* @author Jim McMaster
* @author Jige Yu
* @since 10.0
*/
@Beta
@GwtCompatible
public final class EqualsTester {
private static final int REPETITIONS = 3;
private final List<List<Object>> equalityGroups = Lists.newArrayList();
/**
* Constructs an empty EqualsTester instance
*/
public EqualsTester() {}
/**
* Adds {@code equalityGroup} with objects that are supposed to be equal to
* each other and not equal to any other equality groups added to this tester.
*/
public EqualsTester addEqualityGroup(Object... equalityGroup) {
checkNotNull(equalityGroup);
equalityGroups.add(ImmutableList.copyOf(equalityGroup));
return this;
}
/**
* Run tests on equals method, throwing a failure on an invalid test
*/
public EqualsTester testEquals() {
RelationshipTester<Object> delegate = new RelationshipTester<Object>(
new RelationshipAssertion<Object>() {
@Override public void assertRelated(Object item, Object related) {
assertEquals("$ITEM must be equal to $RELATED", item, related);
int itemHash = item.hashCode();
int relatedHash = related.hashCode();
assertEquals("the hash (" + itemHash + ") of $ITEM must be equal to the hash ("
+ relatedHash +") of $RELATED", itemHash, relatedHash);
}
@Override public void assertUnrelated(Object item, Object unrelated) {
// TODO(cpovirk): should this implementation (and
// RelationshipAssertions in general) accept null inputs?
assertTrue("$ITEM must be unequal to $UNRELATED", !Objects.equal(item, unrelated));
}
});
for (List<Object> group : equalityGroups) {
delegate.addRelatedGroup(group);
}
for (int run = 0; run < REPETITIONS; run++) {
testItems();
delegate.test();
}
return this;
}
private void testItems() {
for (Object item : Iterables.concat(equalityGroups)) {
assertTrue(item + " must be unequal to null", !item.equals(null));
assertTrue(item + " must be unequal to an arbitrary object of another class",
!item.equals(NotAnInstance.EQUAL_TO_NOTHING));
assertEquals(item + " must be equal to itself", item, item);
assertEquals("the hash of " + item + " must be consistent", item.hashCode(), item.hashCode());
}
}
/**
* Class used to test whether equals() correctly handles an instance
* of an incompatible class. Since it is a private inner class, the
* invoker can never pass in an instance to the tester
*/
private enum NotAnInstance {
EQUAL_TO_NOTHING;
}
}
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