Mopy/ # no init.py !
   bash/
     __init__.py
     bash.py # <--- Edit: yep there is such a module too
     bass.py
     bosh/
       __init__.py # contains from .. import bass
       bsa_files.py
     ...
   test_bash
     __init__.py # code below
     test_bosh
       __init__.py
       test_bsa_files.py

import sys
from os.path import dirname, abspath, join, sep
mopy = dirname(dirname(abspath(__file__)))
assert mopy.split(sep)[-1].lower() == 'mopy'
sys.path.append(mopy)
print 'Mopy folder appended to path: ', mopy

import unittest
from unittest import TestCase

import bosh

class TestBSAHeader(TestCase):
    def test_read_header(self):
        bosh.bsa_files.Header.read_header()

if __name__ == '__main__':
    unittest.main()

python.exe "C:_JetBrainsPyCharm 2016.2.2helperspycharmutrunner.py" C:pathtoMopytest_bashtest_boshtest_bsa_files.py true

Traceback (most recent call last):
  File "C:_JetBrainsPyCharm 2016.2.2helperspycharmutrunner.py", line 124, in <module>
    modules = [loadSource(a[0])]
  File "C:_JetBrainsPyCharm 2016.2.2helperspycharmutrunner.py", line 43, in loadSource
    module = imp.load_source(moduleName, fileName)
  File "C:Dropboxeclipse_workspacespythonwrye-bashMopytest_bashtest_boshtest_bsa_files.py", line 4, in <module>
    import bosh
  File "C:Dropboxeclipse_workspacespythonwrye-bashMopybashbosh__init__.py", line 50, in <module>
    from .. import bass
ValueError: Attempted relative import beyond toplevel package

if __name__ == '__main__':
    main()

C:_Python27python.exe "C:_JetBrainsPyCharm 2016.2.2helperspycharmutrunner.py" C:Dropboxeclipse_workspacespythonwrye-bashMopytest_bashtest_boshtest_bsa_files.py true
Testing started at 3:45 PM ...
usage: utrunner.py [-h] [-o OBLIVIONPATH] [-p PERSONALPATH] [-u USERPATH]
                   [-l LOCALAPPDATAPATH] [-b] [-r] [-f FILENAME] [-q] [-i]
                   [-I] [-g GAMENAME] [-d] [-C] [-P] [--no-uac] [--uac]
                   [--bashmon] [-L LANGUAGE]
utrunner.py: error: unrecognized arguments: C:Dropboxeclipse_workspacespythonwrye-bashMopytest_bashtest_boshtest_bsa_files.py true

Process finished with exit code 2

import bash.bosh

from bash import bosh

# test_bash__init__.py
sys.path.insert(0, mopy)

import bosh

from .. import bass

import bash.bosh

from .. import bass