[Zope-CMF] how can I fake authentication in a unit test case

[robert]

Hi there,

in a complex environment with a bunch of groups , rules and folders I 
would like to programmatically test that every combination of 
user/role/document is properly handled permission wise.

To do this I would like to have a unit test with a testusers that tries 
to handle documents according to his roles.

Now my question:
how can a testuser authenticate itself in a unit test?

Or is there some other way to achieve this goal?

thanks for your tips

Robert