assertEquals(ImmutableMap.of(6, "z"), diff1.entriesOnlyOnRight());
    assertEquals(ImmutableMap.of(1, "a"), diff1.entriesInCommon());
    assertEquals(
        ImmutableMap.of(
            3, ValueDifferenceImpl.create("c", "f"), 5, ValueDifferenceImpl.create("e", "g")),
        diff1.entriesDiffering());
    assertEquals(
        "not equal: only on left={2=b, 4=d}: only on right={6=z}: "
            + "value differences={3=(c, f), 5=(e, g)}",

    assertEquals(ImmutableMap.of(6, "z"), diff1.entriesOnlyOnRight());
    assertEquals(ImmutableMap.of(1, "a"), diff1.entriesInCommon());
    assertEquals(
        ImmutableMap.of(
            3, ValueDifferenceImpl.create("c", "f"), 5, ValueDifferenceImpl.create("e", "g")),
        diff1.entriesDiffering());
    assertEquals(
        "not equal: only on left={2=b, 4=d}: only on right={6=z}: "
            + "value differences={3=(c, f), 5=(e, g)}",

    }
  }

  static class ValueDifferenceImpl<V extends @Nullable Object>
      implements MapDifference.ValueDifference<V> {
    @ParametricNullness private final V left;
    @ParametricNullness private final V right;

    static <V extends @Nullable Object> ValueDifference<V> create(
        @ParametricNullness V left, @ParametricNullness V right) {
      return new ValueDifferenceImpl<>(left, right);
    }