The can_move(piece, from, to, colour) function can be called to validate a move. True means the move is allowed, False means the move is not allowed, and None means your move is invalid (e.g. off the board).
Unit tests can be run using pytest. If you're not a Python/pipenv user, then the following commands will run the unit tests:
# Install pipenv to manage dependencies nicely
pip install pipenv
# Run tests, making sure the pytest dependency is installed in a virtual environment for cleanliness
pipenv run pytest chess.py