How to write tests for a Python 3 project not installed by pip

I have a project with a structure like this:

readme.md
requirements.txt
project/
    main.py
    helpers.py
    recording.py

I want to write some tests, for example test_helpers.py that will test the functionaility in helpers.py

I tried doing it like this:

readme.md
requirements.txt
project/
    __init__.py
    main.py
    helpers.py
    recording.py
tests/
    test_helpers.py

and in test_helpers.py:

from ..project import helpers

But this throws an error:

ImportError: attempted relative import with no known parent package

How would I go about importing things correctly?

I'm aware that I can add the directory using sys.path.insert but that seems quite hacky considering I would have to do it for every test*.py file?