Testing JupyterHub and linting code#

Unit testing helps to validate that JupyterHub works the way we think it does, and continues to do so when changes occur. They also help communicate precisely what we expect our code to do.

JupyterHub uses pytest for all the tests. You can find them under the jupyterhub/tests directory in the git repository.

Running the tests#

Make sure you have completed Setting up a development install. Once you are done, you would be able to run jupyterhub from the command line and access it from your web browser. This ensures that the dev environment is properly set up for tests to run.
You can run all tests in JupyterHub
```
pytest -v jupyterhub/tests
```
This should display progress as it runs all the tests, printing information about any test failures as they occur.

If you wish to confirm test coverage the run tests with the --cov flag:
```
pytest -v --cov=jupyterhub jupyterhub/tests
```

You can also run tests in just a specific file:

pytest -v jupyterhub/tests/<test-file-name>

To run a specific test only, you can do:
```
pytest -v jupyterhub/tests/<test-file-name>::<test-name>
```
This runs the test with function name <test-name> defined in <test-file-name>. This is very useful when you are iteratively developing a single test.

For example, to run the test test_shutdown in the file test_api.py, you would run:
```
pytest -v jupyterhub/tests/test_api.py::test_shutdown
```
For more details, refer to the pytest usage documentation.

Test organisation#

The tests live in jupyterhub/tests and are organized roughly into:

test_api.py tests the REST API
test_pages.py tests loading the HTML pages

and other collections of tests for different components. When writing a new test, there should usually be a test of similar functionality already written and related tests should be added nearby.

The fixtures live in jupyterhub/tests/conftest.py. There are fixtures that can be used for JupyterHub components, such as:

app: an instance of JupyterHub with mocked parts
auth_state_enabled: enables persisting auth_state (like authentication tokens)
db: a sqlite in-memory DB session
io_loop`: a Tornado event loop
event_loop: a new asyncio event loop
user: creates a new temporary user
admin_user: creates a new temporary admin user
single user servers - cleanup_after: allows cleanup of single user servers between tests
mocked service - MockServiceSpawner: a spawner that mocks services for testing with a short poll interval - mockservice`: mocked service with no external service url - mockservice_url: mocked service with a url to test external services

And fixtures to add functionality or spawning behavior:

admin_access: grants admin access
no_patience`: sets slow-spawning timeouts to zero
slow_spawn: enables the SlowSpawner (a spawner that takes a few seconds to start)
never_spawn: enables the NeverSpawner (a spawner that will never start)
bad_spawn: enables the BadSpawner (a spawner that fails immediately)
slow_bad_spawn: enables the SlowBadSpawner (a spawner that fails after a short delay)

Refer to the pytest fixtures documentation to learn how to use fixtures that exists already and to create new ones.

Troubleshooting Test Failures#

All the tests are failing#

Make sure you have completed all the steps in Setting up a development install successfully, and are able to access JupyterHub from your browser at http://localhost:8000 after starting jupyterhub in your command line.

Code formatting and linting#

JupyterHub automatically enforces code formatting. This means that pull requests with changes breaking this formatting will receive a commit from pre-commit.ci automatically.

To automatically format code locally, you can install pre-commit and register a git hook to automatically check with pre-commit before you make a commit if the formatting is okay.

pip install pre-commit
pre-commit install --install-hooks

To run pre-commit manually you would do:

# check for changes to code not yet committed
pre-commit run

# check for changes also in already committed code
pre-commit run --all-files

You may also install black integration into your text editor to format code automatically.