001/*
002 * Copyright (C) 2008 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.collect.testing.testers;
018
019import static com.google.common.collect.testing.Helpers.getMethod;
020
021import com.google.common.annotations.GwtCompatible;
022import com.google.common.annotations.GwtIncompatible;
023import com.google.common.annotations.J2ktIncompatible;
024import java.lang.reflect.Method;
025import org.junit.Ignore;
026
027/**
028 * Tests {@link java.util.List#hashCode}.
029 *
030 * @author George van den Driessche
031 */
032@GwtCompatible(emulated = true)
033@Ignore("test runners must not instantiate and run this directly, only via suites we build")
034// @Ignore affects the Android test runner, which respects JUnit 4 annotations on JUnit 3 tests.
035@SuppressWarnings("JUnit4ClassUsedInJUnit3")
036public class ListHashCodeTester<E> extends AbstractListTester<E> {
037  public void testHashCode() {
038    int expectedHashCode = 1;
039    for (E element : getOrderedElements()) {
040      expectedHashCode = 31 * expectedHashCode + ((element == null) ? 0 : element.hashCode());
041    }
042    assertEquals(
043        "A List's hashCode() should be computed from those of its elements.",
044        expectedHashCode,
045        getList().hashCode());
046  }
047
048  /**
049   * Returns the {@link Method} instance for {@link #testHashCode()} so that list tests on
050   * unhashable objects can suppress it with {@code FeatureSpecificTestSuiteBuilder.suppressing()}.
051   */
052  @J2ktIncompatible
053  @GwtIncompatible // reflection
054  public static Method getHashCodeMethod() {
055    return getMethod(ListHashCodeTester.class, "testHashCode");
056  }
057}