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// Copyright 2017 The Bazel Authors. All rights reserved.
//
// 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.devtools.build.lib.rules.apple;
import static com.google.common.truth.Truth.assertThat;
import static org.junit.Assert.fail;
import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableList;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import javax.annotation.Nullable;
/**
* Tests that a given comparator (or the implementation of {@link Comparable}) is correct. To use,
* repeatedly call {@link #addEqualityGroup(Object...)} with sets of objects that should be equal.
* The calls to {@link #addEqualityGroup(Object...)} must be made in sorted order. Then call {@link
* #testCompare()} to test the comparison. For example:
*
* <pre>{@code
* new ComparatorTester()
* .addEqualityGroup(1)
* .addEqualityGroup(2)
* .addEqualityGroup(3)
* .testCompare();
* }</pre>
*/
public class ComparatorTester {
@SuppressWarnings({"unchecked", "rawtypes"})
private final @Nullable Comparator comparator;
/** The items that we are checking, stored as a sorted set of equivalence classes. */
private final List<List<Object>> equalityGroups;
/**
* Creates a new instance that tests the order of objects using the natural order (as defined by
* {@link Comparable}).
*/
public ComparatorTester() {
this(null);
}
/**
* Creates a new instance that tests the order of objects using the given comparator. Or, if the
* comparator is {@code null}, the natural ordering (as defined by {@link Comparable})
*/
public ComparatorTester(@Nullable Comparator<?> comparator) {
this.equalityGroups = new ArrayList<>();
this.comparator = comparator;
}
/**
* Adds a set of objects to the test which should all compare as equal. All of the elements in
* {@code objects} must be greater than any element of {@code objects} in a previous call to
* {@link #addEqualityGroup(Object...)}.
*
* @return {@code this} (to allow chaining of calls)
*/
public ComparatorTester addEqualityGroup(Object... objects) {
Preconditions.checkNotNull(objects);
Preconditions.checkArgument(objects.length > 0, "Array must not be empty");
equalityGroups.add(ImmutableList.copyOf(objects));
return this;
}
@SuppressWarnings({"unchecked", "rawtypes"})
private int compare(Object a, Object b) {
int compareValue;
if (comparator == null) {
compareValue = ((Comparable) a).compareTo(b);
} else {
compareValue = comparator.compare(a, b);
}
return compareValue;
}
public final void testCompare() {
for (int referenceIndex = 0; referenceIndex < equalityGroups.size(); referenceIndex++) {
for (Object reference : equalityGroups.get(referenceIndex)) {
testNullCompare(reference);
testClassCast(reference);
for (int otherIndex = 0; otherIndex < equalityGroups.size(); otherIndex++) {
for (Object other : equalityGroups.get(otherIndex)) {
assertThat(compare(reference, other))
.isEqualTo(Integer.compare(referenceIndex, otherIndex));
}
}
}
}
}
private void testNullCompare(Object obj) {
// Comparator does not require any specific behavior for null.
if (comparator == null) {
try {
compare(obj, null);
fail("Expected NullPointerException in " + obj + ".compare(null)");
} catch (NullPointerException expected) {
}
}
}
@SuppressWarnings("unchecked")
private void testClassCast(Object obj) {
if (comparator == null) {
try {
compare(obj, ICanNotBeCompared.INSTANCE);
fail("Expected ClassCastException in " + obj + ".compareTo(otherObject)");
} catch (ClassCastException expected) {
}
}
}
private static final class ICanNotBeCompared {
static final ComparatorTester.ICanNotBeCompared INSTANCE = new ICanNotBeCompared();
}
}
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