'Test all permutations of N-combinations of numeric types and ensure
that the order of types in the sequence is irrelevant.'

def unify_number_pair_test(self, n):

    ctx = typing.Context()
    for tys in itertools.combinations(types.number_domain, n):
        res = [ctx.unify_types(*comb) for comb in itertools.permutations(tys)]
        first_result = res[0]
        self.assertIsInstance(first_result, types.Number)
        for other in res[1:]:
            self.assertEqual(first_result, other)
