AttributeError: 'module' object has no attribute '__path__'

I am sorry for the dumb question, but I have been banging my head against a wall for past two hours.

I want to use relative imports and my project structure looks like this:

auto_testing
+ tests
  + __init__.py
  + my_module.py
+ src
  + __init__.py
  + my_module.py
+ __init__.py

The contents of tests/my_module.py are:

import unittest

from src.my_module import MyClass

class TestMyClass(unittest.TestCase):
    def setUp(self):
        self.inst = MyClass()

    def test_division_by_zero(self):
        self.assertRaises(ZeroDivisionError, self.inst.divide, 1, 0)

def run_tests():
    unittest.main()

if __name__ == '__main__':
    run_tests()

Then I run commands in terminal

cd auto_testing
python3 -m tests.my_module

and get Error while finding spec for 'tests.my_module.py' (<class 'AttributeError'>: 'module' object has no attribute '__path__').

When I run

cd auto_testing
python3
import tests.my_module
tests.my_module.run_tests()

I get Ran 0 tests (why no tests were found should be another question, but the point is, that MyClass is imported properly and unittest.main() seems to be called; checked with print).

Should I go sleeping for I missed something very simple?