Testing your code

As it states in the Style guidelines section all code is checked to verify the following:

  • All the unit tests pass
  • All code passes the checks from the linting tools

Local testing is done using Tox, which has been installed as part of running script/setup in the virtual environment. To start the tests, activate the virtual environment and simply run the command:


It might be required that you install additional packages depending on your distribution/operating system:

  • Fedora: sudo dnf -y install systemd-devel gcc-c++
  • Ubuntu: sudo apt-get install libudev-dev

Important: Run tox before you create your pull request to avoid annoying fixes.

Running tox will run unit tests against the locally available Python releases, as well as validate the code and document style using pycodestyle, pydocstyle and pylint. You can run tests on only one tox target -- just use -e to select an environment. For example, tox -e lint runs the linters only, and tox -e py38 runs unit tests only on Python 3.8.

tox uses virtual environments under the hood to create isolated testing environments. The tox virtual environments will get out-of-date when requirements change, causing test errors. Run tox -r to tell tox to recreate the virtual environments.

macOS users may see an Error creating virtualenv when runnng tox. If this occurs, install the tox-venv package using the command pip install tox-venv and try again.

Adding new dependencies to test environment

If you are working on tests for an integeration and you need the dependencies available inside the tox environment, update the list inside script/gen_requirements_all.py. Then run the script and then run tox -r to recreate the virtual environments.

Running single tests using tox

You can pass arguments via tox to py.test to be able to run single test suites or test files. Replace py38 with the Python version that you use.

# Stop after the first test fails
$ tox -e py38 -- tests/test_core.py -x
# Run test with specified name
$ tox -e py38 -- tests/test_core.py -k test_split_entity_id
# Fail a test after it runs for 2 seconds
$ tox -e py38 -- tests/test_core.py --timeout 2
# Show the 10 slowest tests
$ tox -e py38 -- tests/test_core.py --duration=10

Testing outside of Tox

Running tox will invoke the full test suite. Even if you specify which tox target to run, you still run all tests inside that target. That's not very convenient to quickly iterate on your code! To be able to run the specific test suites without tox, you'll need to install the test dependencies into your Python environment:

pip3 install -r requirements_test_all.txt -c homeassistant/package_constraints.txt

Now that you have all test dependencies installed, you can run tests on individual files:

flake8 homeassistant/core.py
pylint homeassistant/core.py
pydocstyle homeassistant/core.py
py.test tests/test_core.py

You can also run linting tests against all changed files, as reported by git diff upstream/dev... --diff-filter=d --name-only, using the lint script:


Preventing linter errors

Save yourself the hassle of extra commits just to fix style errors by enabling the Flake8 git commit hook. Flake8 will check your code when you try to commit to the repository and block the commit if there are any style errors, which gives you a chance to fix them!

pip3 install flake8 flake8-docstrings
flake8 --install-hook=git

The flake8-docstrings extension will check docstrings according to PEP257 when running Flake8.

Notes on PyLint and PEP8 validation

If you can't avoid a PyLint warning, add a comment to disable the PyLint check for that line with # pylint: disable=YOUR-ERROR-NAME. Example of an unavoidable one is if PyLint incorrectly reports that a certain object doesn't have a certain member.

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