Actually here, the fact that here Configurable and Magic are on both side of `generate_magic` make the following test fails.
```
def test_script_config():
    ip = get_ipython()
    ip.config.ScriptMagics.script_magics = ['whoda']
    sm = script.ScriptMagics(shell=ip)
    nt.assert_in('whoda', sm.magics['cell'])
```

There is no way to have back current behavior which is to have `whoda` defined as well as other script magics. 
Actually I don't really understand why this works as it does on current master. I would expect `whoda` to be the only defined script magic in this test.