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

  public void testSingletonBuilder() {
    ImmutableBiMap<String, Integer> map = new Builder<String, Integer>().put("one", 1).build();
    assertMapEquals(map, "one", 1);
    assertMapEquals(map.inverse(), 1, "one");
  }

    ImmutableSortedMap<String, Integer> map =
        ImmutableSortedMap.<String, Integer>naturalOrder().build();
    assertEquals(Collections.<String, Integer>emptyMap(), map);
  }

  public void testSingletonBuilder() {
    ImmutableSortedMap<String, Integer> map =
        ImmutableSortedMap.<String, Integer>naturalOrder().put("one", 1).build();
    assertMapEquals(map, "one", 1);
  }

  public void testBuilder() {