/*
    * Copyright (C) 2008 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.collect.testing.testers;
  
  import static com.google.common.collect.testing.features.CollectionFeature.ALLOWS_NULL_VALUES;
  
  import com.google.common.annotations.GwtCompatible;
  import com.google.common.collect.testing.features.CollectionFeature;
  import com.google.common.collect.testing.features.CollectionSize;
  
  import java.util.Collection;
  
  /**
   * Tests {@link java.util.Set#hashCode}.
   *
   * @author George van den Driessche
   */
  @GwtCompatible(emulated = true)
  public class SetHashCodeTester<E> extends AbstractSetTester<E> {
    public void testHashCode() {
      int expectedHashCode = 0;
      for (E element : getSampleElements()) {
        expectedHashCode += ((element == null) ? 0 : element.hashCode());
      }
      assertEquals(
          "A Set's hashCode() should be the sum of those of its elements.",
          expectedHashCode, getSet().hashCode());
    }
  
    @CollectionSize.Require(absent = CollectionSize.ZERO)
    @CollectionFeature.Require(ALLOWS_NULL_VALUES)
    public void testHashCode_containingNull() {
      Collection<E> elements = getSampleElements(getNumElements() - 1);
      int expectedHashCode = 0;
      for (E element : elements) {
        expectedHashCode += ((element == null) ? 0 : element.hashCode());
      }
  
      elements.add(null);
      collection = getSubjectGenerator().create(elements.toArray());
      assertEquals(
          "A Set's hashCode() should be the sum of those of its elements (with "
              + "a null element counting as having a hash of zero).",
          expectedHashCode, getSet().hashCode());
    }
  }