<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def with_args_validator(self, matching_function):
 """Define a custom function for testing arguments :param func matching_function: The function used to test arguments passed to the stub. """

        self.args = None
        self.kwargs = None
        self._custom_matcher = matching_function
        return self