[Tutor] import issues

[James Hartley]

 I admit that I have not internalized how Python's import system works yet.
Given the following directory structure:

+-project
    |
    +-src
    |   |
    |   +-__init__.py
    |   +-foo.py
    |
    +-tests
        |
        +-test_foo.py

Currently, __init__.py is empty.  What needs to be placed in __init__.py
and test_foo.py in order for pytest to execute all tests in test_foo.py?
pytest is being executed while in the project directory.  With:

from foo import Foo

--or--

from src.foo import Foo

defined in test_foo.py, pytest reports "ModuleNotFoundError: No module
named 'src'".

Any and all comments would be appreciated.  Any links to online sources
would also be appreciated. Thanks!

j