def test_tween_sorting_one_tween():
    reg = TweenRegistry()

    def foo():
        pass

    reg.register_tween_factory(foo, over=None, under=None)
    assert reg.sorted_tween_factories() == [foo]

def test_tween_sorting_dag_error2():
    reg = TweenRegistry()

    def a():
        pass

    reg.register_tween_factory(a, over=a, under=None)

    with pytest.raises(TopologicalSortError):
        reg.sorted_tween_factories()

def test_tween_sorting_two_tweens_over_reverse_reg():
    reg = TweenRegistry()

    def top():
        pass

    def bottom():
        pass

    reg.register_tween_factory(bottom, over=None, under=None)
    reg.register_tween_factory(top, over=bottom, under=None)
    assert reg.sorted_tween_factories() == [top, bottom]

def test_tween_sorting_three():
    reg = TweenRegistry()

    def a():
        pass

    def b():
        pass

    def c():
        pass

    reg.register_tween_factory(a, over=None, under=None)
    reg.register_tween_factory(b, over=None, under=a)
    reg.register_tween_factory(c, over=a, under=None)
    assert reg.sorted_tween_factories() == [c, a, b]

def test_tween_sorting_no_tweens():
    reg = TweenRegistry()
    assert reg.sorted_tween_factories() == []