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

  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