def test_cast():
    assert (bool(Interval.empty()) is False)
    assert (bool(Interval(0, 0)) is True)
    assert (list(Interval.empty()) == [])
    assert (list(Interval(0, 0)) == [0, 0])
    assert (list(Interval.open(1, 20)) == [1, 20])
def test_cast():
    assert (bool(Interval.empty()) is False)
    assert (bool(Interval(0, 0)) is True)
    assert (list(Interval.empty()) == [])
    assert (list(Interval(0, 0)) == [0, 0])
    assert (list(Interval.open(1, 20)) == [1, 20])