There are similar questions but none of them have a completly sibling test folder with main.py in the src folder and none of them work. Currently I use the following approach #project/tests/aaa/bbb/test_foo.py import unittest import sys sys.path.append("....") from src.aaa.bbb import foo as foo #... and end up with a ModuleNotFoundError: No module named 'src' (I tested profoundly if the amount of points in sys.path.append("....") is correct) Maybe I do not understand python but my folder structures (which I would like to keep) goes: /project /src main.py /aaa /bbb foo.py /tests /aaa /bbb test_foo.py I execute it in the project folder and for the normal not-test files that works fine. A former Try was (in test_foo.py): from ....src.aaa.bbb import foo as foo This is the approach that works in the normal files but for the test files I got: ImportError: attempted relative import with no known parent package `` I tried it with and without the ``` -m``` option. Also with and without if __name__ == '__main__': unittest.main() Continue reading...