def METHOD_NAME(self):
    c = Composition({"Fe": 4, "O": 16, "P": 4})
    charge = 4
    assert Ion(c, charge).formula == "Fe4 P4 O16 +4"
    f = {1: 1, 8: 1}
    charge = -1
    assert Ion(Composition(f), charge).formula == "H1 O1 -1"
    assert Ion(Composition(S=2, O=3), -2).formula == "S2 O3 -2"