human
Solve the following python programming problem given the following code:
def assertResponse(self, expected_status, expected_headers, expected_content, fn, * args, **kwargs) : 
    "Calls fn(*args, <start_response>, **kwargs) and checks the result.

    Args:
      expected_status: The expected HTTP status returned e.g. '200 OK'.
      expected_headers: A dict, list or wsgiref.headers.Headers representing the
          expected generated HTTP headers e.g. {'Content-type': 'text/plain'}.
      expected_content: The expected content generated e.g. 'Hello World'.
      fn: The function to test. This function will be called with
          fn(*args, start_response=<func>, **kwargs) where the start_response
          function verifies that it is called with the correct status and
          headers.
      *args: The positional arguments passed to fn.
      **kwargs: The keyword arguments passed to fn.
    " 
    write_buffer = cStringIO.StringIO () 
    def start_response(status, headers, exc_info = None) : 
        self.assertEqual (expected_status, status) 
        self.assertHeadersEqual (expected_headers, headers) 
        self.assertEqual (None, exc_info) 
        return write_buffer.write 
args += (start_response,) 
    response = fn (* args, ** kwargs) 
    self.assertNotEqual (None, response, ('%r(*args, **kwargs) != None' % fn)) 
    response = ''.join (start_response) 
    self.assertIsInstance (response, str, ('response %r must be a str' % response [: 10])) 
    self.assertMultiLineEqual (expected_content, (write_buffer.getvalue () + response)) 

    
    

    Fix the buggy line: response = ''.join (start_response)
assistant
#Here is Python program to fix the buggy line: response = ''.

response = ''.join (response)