human
Solve the following python programming problem given the following code:
def testUndo(self) : 
    s = Gaffer.ScriptNode () 
    s ['b'] = Gaffer.Box () 
    s ['b'] ['p'] = Gaffer.Plug (flags = (Gaffer.Plug.Flags.Default | Gaffer.Plug.Flags.Dynamic)) 
    s ['b'].exportForReference ('/tmp/test.grf') 
    s ['r'] = Gaffer.Reference () 
    self.assertEqual (s ['r'].fileName (), '') 
    self.assertTrue (('p' not in s ['r'])) 
    State = collections.namedtuple ('State', ['keys', 'fileName']) 
    states = [] 
    def referenceLoaded(node) : 
        states.append (State (keys = node.keys (), fileName = node.fileName ())) 
c = s ['r'].referenceLoadedSignal ().connect (referenceLoaded) 
    with Gaffer.UndoContext (s) : 
        s ['r'].load ('/tmp/test.grf') 
self.assertTrue (('p' in s ['r'])) 
    self.assertEqual (s ['r'].fileName (), '/tmp/test.grf') 
    self.assertTrue (len (states), 1) 
    self.assertEqual (states [0], State (['user', 'p'], '/tmp/test.grf')) 
    s.undo () 
    self.assertEqual (s ['r'].fileName (), '') 
    self.assertTrue (('p' not in self ['r'])) 
    self.assertTrue (len (states), 2) 
    self.assertEqual (states [1], State (['user'], '')) 
    s.redo () 
    self.assertTrue (('p' in s ['r'])) 
    self.assertEqual (s ['r'].fileName (), '/tmp/test.grf') 
    self.assertTrue (len (states), 3) 
    self.assertEqual (states [2], State (['user', 'p'], '/tmp/test.grf')) 

    
    

    Fix the buggy line: self.assertTrue (('p' not in self ['r']))
assistant
#Here is Python program to fix the buggy line: self.

self.assertTrue (('p' not in s ['r']))