assertThat(ArbitraryInstances.get(int[].class)).isEmpty();
    assertThat(ArbitraryInstances.get(Object[].class)).isEmpty();
    assertThat(ArbitraryInstances.get(String[].class)).isEmpty();
  }

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

  public void testGet_interface() {