if (this.length() != that.length()) {
      return false;
    }
    for (int i = 0; i < length(); i++) {
      if (!areEqual(this.get(i), that.get(i))) {
        return false;
      }
    }
    return true;
  }

  // Match the behavior of Double.equals()
  private static boolean areEqual(double a, double b) {
    return Double.doubleToLongBits(a) == Double.doubleToLongBits(b);
  }

  private static final Map<Integer, Integer> SINGLETON = singletonMap(1, 2);

  public void testMapDifferenceEmptyEmpty() {
    MapDifference<Integer, Integer> diff = Maps.difference(EMPTY, EMPTY);
    assertTrue(diff.areEqual());
    assertEquals(EMPTY, diff.entriesOnlyOnLeft());
    assertEquals(EMPTY, diff.entriesOnlyOnRight());
    assertEquals(EMPTY, diff.entriesInCommon());
    assertEquals(EMPTY, diff.entriesDiffering());

    assertTrue(ArbitraryInstances.get(ImmutableSetMultimap.class).isEmpty());
    assertTrue(ArbitraryInstances.get(MapDifference.class).areEqual());
    assertTrue(ArbitraryInstances.get(SortedMapDifference.class).areEqual());
    assertEquals(Range.all(), ArbitraryInstances.get(Range.class));
    assertTrue(ArbitraryInstances.get(NavigableSet.class).isEmpty());

    assertTrue(ArbitraryInstances.get(ImmutableSetMultimap.class).isEmpty());
    assertTrue(ArbitraryInstances.get(MapDifference.class).areEqual());
    assertTrue(ArbitraryInstances.get(SortedMapDifference.class).areEqual());
    assertEquals(Range.all(), ArbitraryInstances.get(Range.class));
    assertTrue(ArbitraryInstances.get(NavigableSet.class).isEmpty());

      this.onlyOnRight = unmodifiableMap(onlyOnRight);
      this.onBoth = unmodifiableMap(onBoth);
      this.differences = unmodifiableMap(differences);
    }

    @Override
    public boolean areEqual() {
      return onlyOnLeft.isEmpty() && onlyOnRight.isEmpty() && differences.isEmpty();
    }

    @Override
    public Map<K, V> entriesOnlyOnLeft() {
      return onlyOnLeft;
    }

    @Override

      this.onlyOnRight = unmodifiableMap(onlyOnRight);
      this.onBoth = unmodifiableMap(onBoth);
      this.differences = unmodifiableMap(differences);
    }

    @Override
    public boolean areEqual() {
      return onlyOnLeft.isEmpty() && onlyOnRight.isEmpty() && differences.isEmpty();
    }

    @Override
    public Map<K, V> entriesOnlyOnLeft() {
      return onlyOnLeft;
    }

    @Override