Python unittest fails with No module loaded in VScode

Question

I have the following directory structure

when I use the test runner I get

File "/home/kyle/dev/tests/test_foo.py", line 2, in <module> import foo ModuleNotFoundError: No module named 'foo'

I'm at a loss as what could be wrong. The test code looks like:

import unittest
import foo

class TestStringMethods(unittest.TestCase):

    def test_upper(self):
        self.assertEqual(foo.f(), 'FOO3')

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

I'm using a virtual environment (.venv) I've set that to my interpreter.

Answer 1

The error happens because foo.py lives under src/, but when you run your tests Python doesn’t automatically know to look there. By default it only searches the current directory, the standard library, and installed site-packages.

From the project root, run the following command to fix:

PYTHONPATH=src python -m unittest discover tests

• PYTHONPATH=src tells Python “also look in the src/ directory when resolving imports.”

• -m unittest discover tests makes unittest discover and run all test files under tests/.

Now import foo will work because src/foo.py is on the import path.