human
Solve the following python programming problem given the following code:
@ test.raises (HookTestException) 
def test_register_hooks_meta(self) : 
    def my_custom_hook_func() : 
        raise HookTestException ('OK') 
app = self.make_app (APP, define_hooks = ['my_custom_hook'], hooks = [('my_custom_hook', <MASK>)]) 
    app.setup () 
    for res in hook.run ('my_custom_hook') : 
        pass 
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is a proper replacement for <MASK>.
def my_custom_hook_func(