assertEquals(Collections.<String, Integer>emptyMap(), copy);
    assertThat(ImmutableBiMap.copyOf(copy)).isSameInstanceAs(copy);
    assertThat(copy).isSameInstanceAs(ImmutableBiMap.of());
  }

  public void testCopyOfSingletonMap() {
    ImmutableBiMap<String, Integer> copy = ImmutableBiMap.copyOf(singletonMap("one", 1));
    assertMapEquals(copy, "one", 1);
    assertThat(ImmutableBiMap.copyOf(copy)).isSameInstanceAs(copy);
  }

    assertThat(ImmutableSortedMap.copyOf(copy)).isSameInstanceAs(copy);
    assertThat(copy.comparator()).isEqualTo(Ordering.natural());
  }

  public void testCopyOfSingletonMap() {
    ImmutableSortedMap<String, Integer> copy = ImmutableSortedMap.copyOf(singletonMap("one", 1));
    assertMapEquals(copy, "one", 1);
    assertThat(ImmutableSortedMap.copyOf(copy)).isSameInstanceAs(copy);