# helper class defined elsewhere

class CallLogger(object):

   def __init__(self, meth):

     self.meth = meth

     self.was_called = False

   def __call__(self, code=None):

     self.meth()

     self.was_called = True

然后assert CallLogger的was_called为True就行了。但是这样的Callable不是个函数：

isinstance(object, types.FunctionType) # Callable will be False

对于这种Callable获取参数个数需要用：

inspect.getargspec(fn.__call__)