human
Solve the following python programming problem given the following code:
@ on_linux 
def test_cpu_time(self) : 
    '
        Fake Flocker cluster gives expected results.
        ' 
    clock = Clock () 
    node1 = Node (uuid = uuid4 (), public_address = IPAddress ('10.0.0.1')) 
    node2 = Node (uuid = uuid4 (), public_address = IPAddress ('10.0.0.2')) 
    metric = CPUTime (clock, BenchmarkCluster (IPAddress ('10.0.0.1'), (lambda reactor : FakeFlockerClient ([node1, node2])), { 
        
}, None), _LocalRunner (), processes = [_pid_1_name]) 
    d = metric.measure ((lambda : clock.advance (5))) 
    def remove_process_times(node_cpu_times) : 
        for process_times in node_cpu_times.values () : 
            if process_times : 
                for process in process_times : 
                    if (process != WALLCLOCK_LABEL) : 
                        process_times [process] = 0 
return node_cpu_times 
d.addCallback (<MASK>) 
    def check(result) : 
        self.assertEqual (result, { 
            '10.0.0.1' : { 
                _pid_1_name : 0, 
                WALLCLOCK_LABEL : 5, 
}, 
            '10.0.0.2' : { 
                _pid_1_name : 0, 
                WALLCLOCK_LABEL : 5, 
}, 
}) 
d.addCallback (check) 
    return d 
    
    Given the code above, what is a proper replacement for <MASK>? Choose among: d, node2, clock, check, node1, self, metric
assistant
#Here is a proper replacement for <MASK>.
def remove_process_times(