def test_range(): assert first(range(0)) is None assert first(range(3)) == 0
def test_list(): assert first([]) is None assert first([1, 2, 3]) == 1
def test_dict(): assert first(dict()) is None assert first(dict({"1": 1, "2": 2, "3": 3})) == "1"
def test_str(): assert first("") is None assert first("123") == "1"
def test_set(): assert first({}) is None assert first({1, 2, 3}) == 1
def test_tuple(): assert first(tuple()) is None assert first((1, 2, 3)) == 1