}

  public void testGet_enum() {
    assertNull(ArbitraryInstances.get(EmptyEnum.class));
    assertEquals(Direction.UP, ArbitraryInstances.get(Direction.class));
  }

  public void testGet_interface() {
    assertNull(ArbitraryInstances.get(SomeInterface.class));
  }

  public void testGet_runnable() {
    ArbitraryInstances.get(Runnable.class).run();
  }

  public void testGet_class() {