Map<Class<?>, Object> in = emptyMap();
    ClassToInstanceMap<Object> map = ImmutableClassToInstanceMap.copyOf(in);
    assertTrue(map.isEmpty());
  }

  public void testCopyOf_imap_valid() {
    ImmutableMap<Class<? extends Number>, ? extends Number> in =
        ImmutableMap.of(Number.class, 0, Double.class, Math.PI);
    ClassToInstanceMap<Number> map = ImmutableClassToInstanceMap.copyOf(in);