python unit test not finding another folder module

Question

I have the following folder structure:

sdn_unit_tests/ this contains two folders, 'classes' and 'tests'.

'classes' contains one file 'validator.py' and a pycache folder. 'tests' contains one file 'test_validator.py'

The code for validator.py:

class Validator:

    def username_is_valid(self, username):

        if len(username) > 10:
            return False

        if ' ' in username:
            return False

        if username.islower():
            return False

        return True

The code for test_validator.py:

import unittest

from classes.validator import Validator

class TestValidator(unittest.TestCase):
    def  test_it_will_reject_username_if_too_long(self):#has to start with 'test_'
        #Assume
        username = 'InvalidTooLong'
        validator = Validator()

        #Action
        result = validator.username_is_valid(username)

        #Assert
        self.assertFalse(result)

Expected behaviour: I expect that running test_validator.py will at least find the module, this is my first unit test so I don't know if it will say OK or false but I still expect it to find the classes.validator

Error:

Traceback (most recent call last):
  File "/Users/.../Desktop/sdn_unit_tests/tests/test_validator.py", line 3, in <module>
    from classes.validator import Validator
ModuleNotFoundError: No module named 'classes'

Answer 1

I would recommend running python -m unittest from the parent directory. This will start automatic test discovery. But for this to work, you must create an empty __init__.py file in your tests folder.

Update: as a quick way to run test_validator.py itself (e.g. from an IDE), add this to the beginning:

import sys
sys.path.append('..')

and this to the end:

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