Ahhh I think I understand this now. What you want to test is really that when using `.fred` you get an exception message that is empty when turned into a string. 

In that case, I would change it to this:

```python
        try:
            config_manager.ConfigurationManager(
                (n, getopt,),
                argv_source=['--admin.conf=x.fred']
            )
            assert False, "expected the above to raise an error"
        except AllHandlersFailedException, x:
            self.assertEqual(str(x), '')
        finally:
            os.remove('x.fred')
```

(note removal of variable `cm`)