human
Solve the following python programming problem given the following code:
@ mock.patch.object (greenthread, 'sleep') 
def test_scan_sr_known_error_retries_then_succeeds(self, mock_sleep) : 
    session = mock.Mock () 
    class FakeException (Exception) : 
        details = ['SR_BACKEND_FAILURE_40', '', '', ''] 
session.XenAPI.Failure = FakeException 
    def fake_call_xenapi(* args) : 
        fake_call_xenapi.count += 1 
        if (fake_call_xenapi.count != 2) : 
            raise FakeException () 
fake_call_xenapi.count = 0 
    session.call_xenapi.side_effect = mock_sleep 
    vm_utils._scan_sr (session, 'sr_ref') 
    session.call_xenapi.assert_called_with ('SR.scan', 'sr_ref') 
    self.assertEqual (2, session.call_xenapi.call_count) 
    mock_sleep.assert_called_once_with (2) 

    
    

    Fix the buggy line: session.call_xenapi.side_effect = mock_sleep
assistant
#Here is Python code to fix the buggy line: session.

session.call_xenapi.side_effect = fake_call_xenapi