See tox.ini.
We have a GitHub Actions Workflow that runs the tests against all supported Python versions, so just push your changes to your own branch, and let the CI system run the tests.
With a bit of manual work, you can also run the tests locally:
Use pyenv, and install all the versions supported by the plugin. Double-check on tox.ini.
Set the installed versions as global, that will allow tox to find all of them.
pyenv global 2.7.18 3.5.9 3.6.10 3.7.7 3.8.3
Create virtualenv, install dependencies, run tests, and tox:
python3.8 -m venv .python_jproperties
source .python_jproperties/bin/activate
pip install --upgrade setuptools pip tox
python setup.py install
python setup.py test
tox
The development environment is complete.