human
Solve the following python programming problem given the following code:
@ it ('reports its error on failure') 
def spec(w) : 
    def failed_test_function(self) : 
        assert False 
example = Example ('reports failure', <MASK>) 
    result = example.run (MockExampleGroup (), return_world (w.mock_world)) 
    assert (type (result) == ExampleResult) 
    assert (type (result.exception) is AssertionError) 
    assert (result.traceback is not None) 
    assert (result.kind == 2) 
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is a proper replacement for <MASK>.
def failed_test_function(