def test_dict_properties():
dic = {"length": sympify(1), "time": sympify(2)}
d = Dimension(dic)
assert d["length"] == 1
assert set(d.items()) == set(dic.items())
assert len(d) == 2
assert d.get("length") == 1
assert d.get("mass") is None
assert ("length" in d) is True
assert ("mass" in d) is False
