def test_list_gen_release_id_raise_error_if_id_not_used_already():
    gen = IdListGenerator()
    gen.get_id(16)
    assert_raises(IndexError, lambda: gen.release_id(20))
    assert_raises(IndexError, lambda: gen.release_id(0))
def test_list_gen_release_id_render_it_available():
    gen = IdListGenerator()
    pid = gen.get_id(16)
    gen.release_id(pid)
    assert gen.get_id(pid) == pid