assertThat(e.toString()).isEqualTo("null=null");
    assertEquals(0, e.hashCode());
  }

  /** See {@link SynchronizedBiMapTest} for more tests. */
  @J2ktIncompatible // Synchronized
  public void testSynchronizedBiMap() {
    BiMap<String, Integer> bimap = HashBiMap.create();
    bimap.put("one", 1);
    BiMap<String, Integer> sync = Maps.synchronizedBiMap(bimap);
    bimap.put("two", 2);
    sync.put("three", 3);