You must install the test-runner dependencies:
pip3 install -r tests/requirements.txt
Then make the seedsigner python module visible/importable to the tests by installing it:
pip3 install -e .
Run the whole test suite:
pytest
Run a specific test file:
pytest tests/test_this_file.py
Run a specific test:
pytest tests/test_this_file.py::test_this_specific_test