def METHOD_NAME(self, set_id, error_code=None):
    expected_params = {
        'attachments': [{
            'data': b'This is a sample file for attachment to a support case.',
            'fileName': 'attachment_file.txt'}]}
    response = {'attachmentSetId': set_id}
    self._stub_bifurcator(
        'add_attachments_to_set', expected_params, response, error_code=error_code)