def test_as_arg(self):
        """
        - Is as_arg() and from_arg() implemented?
        - Are they the inverse of each other?
        """
        fnty = ir.FunctionType(ir.VoidType(), [])
        function = ir.Function(self.module, fnty, name="test_as_arg")
        builder = ir.IRBuilder()
        builder.position_at_end(function.append_basic_block())

        undef_value = ir.Constant(self.datamodel.get_value_type(), None)
        args = self.datamodel.as_argument(builder, undef_value)
        self.assertIsNot(args, NotImplemented, "as_argument returned "
                                               "NotImplementedError")

        if isinstance(args, (tuple, list)):
            def recur_tuplize(args, func=None):
                for arg in args:
                    if isinstance(arg, (tuple, list)):
                        yield tuple(recur_tuplize(arg, func=func))
                    else:
                        if func is None:
                            yield arg
                        else:
                            yield func(arg)

            argtypes = tuple(recur_tuplize(args, func=lambda x: x.type))
            exptypes = tuple(recur_tuplize(
                self.datamodel.get_argument_type()))
            self.assertEqual(exptypes, argtypes)
        else:
            self.assertEqual(args.type,
                             self.datamodel.get_argument_type())

        rev_value = self.datamodel.from_argument(builder, args)
        self.assertEqual(rev_value.type, self.datamodel.get_value_type())

        builder.ret_void()  # end function

        # Ensure valid LLVM generation
        materialized = ll.parse_assembly(str(self.module))
        str(materialized)

        - Is as_arg() and from_arg() implemented?
        - Are they the inverse of each other?
        
numba/core/datamodel/testing.py