human
Solve the following python programming problem given the following code:
def test_Valid(self) : 
    'Test that sorting works on a valid graph with one possible order.' 
    graph = { 
        'a' : ['b', 'c'], 
        'b' : [], 
        'c' : ['d'], 
        'd' : ['b'], 
} 
    def GetEdge(node) : 
        return tuple (graph [node]) 
self.assertEqual (gyp.common.TopologicallySorted (graph.keys (), graph), ['a', 'c', 'd', 'b']) 

    
    

    Fix the buggy line: self.assertEqual (gyp.common.TopologicallySorted (graph.keys (), graph), ['a', 'c', 'd', 'b'])
assistant
#Here is Python code to fix the buggy line: self.

self.assertEqual (gyp.common.TopologicallySorted (graph.keys (), def GetEdge(), ['a', 'c', 'd', 'b'])