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.hashCode(
          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.hashCode(
          entriesOnlyOnLeft(), entriesOnlyOnRight(), entriesInCommon(), entriesDiffering());
    }

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