assertSame(
        WithExceptionalConstructor.INSTANCE,
        ArbitraryInstances.get(WithExceptionalConstructor.class));
    assertNull(ArbitraryInstances.get(NonPublicClass.class));
  }

  public void testGet_mutable() {
    assertEquals(0, ArbitraryInstances.get(ArrayList.class).size());
    assertEquals(0, ArbitraryInstances.get(HashMap.class).size());
    assertThat(ArbitraryInstances.get(Appendable.class).toString()).isEmpty();