* #entriesDiffering()} of the two instances are equal.
   */
  @Override
  boolean equals(@Nullable Object object);

  /**
   * Returns the hash code for this instance. This is defined as the hash code of
   *
   * {@snippet :
   * Arrays.asList(entriesOnlyOnLeft(), entriesOnlyOnRight(),
   *     entriesInCommon(), entriesDiffering())
   * }
   */

   * #entriesDiffering()} of the two instances are equal.
   */
  @Override
  boolean equals(@Nullable Object object);

  /**
   * Returns the hash code for this instance. This is defined as the hash code of
   *
   * {@snippet :
   * Arrays.asList(entriesOnlyOnLeft(), entriesOnlyOnRight(),
   *     entriesInCommon(), entriesDiffering())
   * }
   */

    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() {

    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() {

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

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

    @Override

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

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

    @Override