* values.
   */
  Map<K, ValueDifference<V>> entriesDiffering();

  /**
   * Compares the specified object with this instance for equality. Returns {@code true} if the
   * given object is also a {@code MapDifference} and the values returned by the {@link
   * #entriesOnlyOnLeft()}, {@link #entriesOnlyOnRight()}, {@link #entriesInCommon()} and {@link
   * #entriesDiffering()} of the two instances are equal.
   */
  @Override

   * values.
   */
  Map<K, ValueDifference<V>> entriesDiffering();

  /**
   * Compares the specified object with this instance for equality. Returns {@code true} if the
   * given object is also a {@code MapDifference} and the values returned by the {@link
   * #entriesOnlyOnLeft()}, {@link #entriesOnlyOnRight()}, {@link #entriesInCommon()} and {@link
   * #entriesDiffering()} of the two instances are equal.
   */
  @Override

    assertTrue(diff.areEqual());
    assertEquals(EMPTY, diff.entriesOnlyOnLeft());
    assertEquals(EMPTY, diff.entriesOnlyOnRight());
    assertEquals(EMPTY, diff.entriesInCommon());
    assertEquals(EMPTY, diff.entriesDiffering());
    assertEquals("equal", diff.toString());
  }

  public void testMapDifferenceEmptySingleton() {
    MapDifference<Integer, Integer> diff = Maps.difference(EMPTY, SINGLETON);

    assertTrue(diff.areEqual());
    assertEquals(EMPTY, diff.entriesOnlyOnLeft());
    assertEquals(EMPTY, diff.entriesOnlyOnRight());
    assertEquals(EMPTY, diff.entriesInCommon());
    assertEquals(EMPTY, diff.entriesDiffering());
    assertEquals("equal", diff.toString());
  }

  public void testMapDifferenceEmptySingleton() {
    MapDifference<Integer, Integer> diff = Maps.difference(EMPTY, SINGLETON);

            && entriesInCommon().equals(other.entriesInCommon())
            && entriesDiffering().equals(other.entriesDiffering());
      }
      return false;
    }

    @Override
    public int hashCode() {
      return Objects.hash(
          entriesOnlyOnLeft(), entriesOnlyOnRight(), entriesInCommon(), entriesDiffering());
    }

    @Override
    public String toString() {
      if (areEqual()) {

            && entriesInCommon().equals(other.entriesInCommon())
            && entriesDiffering().equals(other.entriesDiffering());
      }
      return false;
    }

    @Override
    public int hashCode() {
      return Objects.hash(
          entriesOnlyOnLeft(), entriesOnlyOnRight(), entriesInCommon(), entriesDiffering());
    }

    @Override
    public String toString() {
      if (areEqual()) {