fail("putIfAbsent(null, value) should throw");
    } catch (NullPointerException expected) {
    }
    expectUnchanged();
    expectNullKeyMissingWhenNullKeysUnsupported(
        "Should not contain null key after unsupported putIfAbsent(null, value)");
  }

  @MapFeature.Require(value = SUPPORTS_PUT, absent = ALLOWS_NULL_VALUES)
  public void testPutIfAbsent_nullValueUnsupported() {
    try {

      fail("putIfAbsent(null, value) should throw");
    } catch (NullPointerException expected) {
    }
    expectUnchanged();
    expectNullKeyMissingWhenNullKeysUnsupported(
        "Should not contain null key after unsupported putIfAbsent(null, value)");
  }

  @MapFeature.Require(value = SUPPORTS_PUT, absent = ALLOWS_NULL_VALUES)
  public void testPutIfAbsent_nullValueUnsupportedAndKeyAbsent() {
    try {

   *
   * <p>The returned supplier is thread-safe. The delegate's {@code get()} method will be invoked at
   * most once unless the underlying {@code get()} throws an exception. The supplier's serialized
   * form does not contain the cached value, which will be recalculated when {@code get()} is called
   * on the deserialized instance.
   *
   * <p>When the underlying delegate throws an exception then this memoizing supplier will keep

          return optional.orNull();
        }
      };

  /**
   * Sets.cartesianProduct doesn't allow sets that contain null, but we want null to mean "don't
   * call the associated CacheBuilder method" - that is, get the default CacheBuilder behavior. This
   * method wraps the elements in the input sets (which may contain null) as Optionals, calls
   * Sets.cartesianProduct with those, then transforms the result to unwrap the Optionals.
   */

    assertTrue("Heap contains 1", mmHeap.remove(1));
    assertFalse("Heap does not contain 1", mmHeap.contains(1));
    assertTrue("Heap contains 2", mmHeap.remove(2));
    assertEquals(0, mmHeap.size());
    assertFalse("Heap does not contain anything", mmHeap.contains(1));
    assertFalse("Heap does not contain anything", mmHeap.remove(2));
  }

  public void testIteratorPastEndException() {

   */
  int size();

  /**
   * Returns {@code true} if this multimap contains no key-value pairs. Equivalent to {@code size()
   * == 0}, but can in some cases be more efficient.
   */
  boolean isEmpty();

  /**
   * Returns {@code true} if this multimap contains at least one key-value pair with the key {@code
   * key}.
   */

   * bimap. Otherwise, the specified map must contain at least one mapping, in order to determine
   * the key type.
   *
   * @param map the map whose mappings are to be placed in this map
   * @throws IllegalArgumentException if map is not an {@code EnumBiMap} or an {@code EnumHashBiMap}
   *     instance and contains no mappings
   */

    assertTrue(
        "addAll(somePresent) should return true",
        collection.addAll(MinimalCollection.of(e3(), e0())));
    assertTrue("should contain " + e3(), collection.contains(e3()));
    assertTrue("should contain " + e0(), collection.contains(e0()));
  }

  @CollectionFeature.Require(absent = SUPPORTS_ADD)
  @CollectionSize.Require(absent = ZERO)
  public void testAddAll_unsupportedSomePresent() {
    try {

          return optional.orNull();
        }
      };

  /**
   * Sets.cartesianProduct doesn't allow sets that contain null, but we want null to mean "don't
   * call the associated CacheBuilder method" - that is, get the default CacheBuilder behavior. This
   * method wraps the elements in the input sets (which may contain null) as Optionals, calls
   * Sets.cartesianProduct with those, then transforms the result to unwrap the Optionals.
   */

   * keys and values are the result of applying the provided mapping functions to the input
   * elements. The generated map is sorted by the specified comparator.
   *
   * <p>If the mapped keys contain duplicates (according to the specified comparator), an {@code
   * IllegalArgumentException} is thrown when the collection operation is performed. (This differs