def test_call():
A = Unit(current)
Js = Unit(action)
mksa = UnitSystem((m, kg, s, A), (Js,))
assert mksa(Js) == mksa.print_unit_base(Js)
assert mksa(Js.dim) == mksa._system(Js.dim)
q = Quantity(10, Js)
assert mksa(q) == "%g %s" % (q.factor, mksa(Js))
