expectThrows(nonEmptyProperSubset);
    expectUnchanged();
  }

  // retainAll(sameElements)

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testRetainAll_sameElements() {
    expectReturnsFalse(sameElements);
    expectUnchanged();
  }

  @CollectionFeature.Require(absent = SUPPORTS_REMOVE)
  public void testRetainAll_sameElementsUnsupported() {