source.py

import pyglet.text as pygtext

class BaseObject(object):
    pass

class Stuff(BaseObject, pygtext.Label):
    pass

tests.py

from mock import Mock

import sys

MOCKS = {
    'pyglet.text': Mock(['Label'])
}

sys.modules.update((mod_name, mod_val) for mod_name, mod_val in MOCKS.items())

import source #see below -- errors about not being able to handle the multiple inheritance

#Traceback (most recent call last):
#  File "tests.py", line 11, in <module>
#    import source #see below -- errors about not being able to handle the multiple inheritance
#  File "/Users/gsmcwhirter/Sources/wwgamelib/tests/source.py", line 6, in <module>
#    class Stuff(BaseObject, pygtext.Label):
#TypeError: Error when calling the metaclass bases
#    metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases