We verify and test Marionette in a couple of different ways, using a combination of unit tests and functional tests. There are three distinct components that we test:

  • the Marionette server, using a combination of xpcshell unit tests and functional tests written in Python spread across Marionette- and WPT tests;
  • the Python client is tested with the same body of functional Marionette tests;
  • and the harness that backs the Marionette, or Mn job on try, tests is verified using separate mock-styled unit tests.

xpcshell unit tests

Marionette has a set of xpcshell unit tests located in _testing/marionette/test/unit. These can be run this way:

% ./mach test testing/marionette/test/unit

Because tests are run in parallel and xpcshell itself is quite chatty, it can sometimes be useful to run the tests sequentially:

% ./mach test --sequential testing/marionette/test/unit/test_error.js

These unit tests run as part of the X jobs on Treeherder.

Marionette functional tests

We also have a set of functional tests that make use of the Marionette Python client. These start a Firefox process and tests the Marionette protocol input and output, and will appear as Mn on Treeherder. The following command will run all tests locally:

% ./mach marionette test

But you can also run individual tests:

% ./mach marionette test testing/marionette/harness/marionette_harness/tests/unit/test_navigation.py

In case you want to run the tests with another Firefox binary:

% ./mach marionette test --binary /path/to/firefox TEST

When working on Marionette it is often useful to surface the stdout from Gecko, which can be achived using the --gecko-log option. See <Debugging.html> for usage instructions, but the gist is that you can redirect all Gecko output to stdout:

% ./mach marionette test --gecko-log - TEST

Our functional integration tests pop up Firefox windows sporadically, and a helpful tip is to suppress the window can be to use Firefox’ headless mode:

% ./mach marionette test -z TEST

-z is an alias for --headless and equivalent to setting the MOZ_HEADLESS output variable. In addition to MOZ_HEADLESS there is also MOZ_HEADLESS_WIDTH and MOZ_HEADLESS_HEIGHT for controlling the dimensions of the no-op virtual display. This is similar to using xvfb(1) which you may know from the X windowing system, but has the additional benefit of also working on macOS and Windows.



  • You have built Fennec with ac_add_options --enable-marionette in your mozconfig.
  • You can run an Android emulator, which means you have the AVD you need.

When running tests on Fennec, you can have Marionette runner take care of starting Fennec and an emulator, as shown below.

% ./mach marionette test --emulator --app fennec
--avd-home /path/to/.mozbuild/android-device/avd
--emulator-binary /path/to/.mozbuild/android-sdk/emulator/emulator

For Fennec tests, if the appropriate emulator command is in your PATH, you may omit the --emulator-binary argument. See ./mach marionette test -h for additional options.

Alternately, you can start an emulator yourself and have the Marionette runner start Fennec for you:

% ./mach marionette test --emulator --app='fennec' --address=localhost:2828 --disable-e10s

To connect to an already-running Fennec in an already running emulator or on a device, you will need to enable Marionette manually by setting the browser preference marionette.enabled set to true in the Fennec profile.

Make sure port 2828 is forwarded:

% adb forward tcp:2828 tcp:2828

If Fennec is already started:

% ./mach marionette test --app='fennec' --address=localhost:2828 --disable-e10s

If Fennec is not already started on the emulator/device, add the --emulator option. Marionette Test Runner will take care of forwarding the port and starting Fennec with the correct prefs. (You may need to run adb forward --remove-all to allow the runner to start.)

% ./mach marionette test --emulator --app='fennec' --address=localhost:2828 --disable-e10s

If you need to troubleshoot the Marionette connection, the most basic check is to start Fennec, make sure the marionette.enabled browser preference is true and port 2828 is forwarded, then see if you get any response from Marionette when you connect manually:

% telnet localhost:2828

You should see output like {"applicationType":"gecko","marionetteProtocol":3}

WPT functional tests

Marionette is also indirectly tested through geckodriver with WPT (Wd on Treeherder). To run them:

% ./mach wpt testing/web-platform/tests/webdriver

WPT tests conformance to the WebDriver standard and uses geckodriver. Together with the Marionette remote protocol in Gecko, they make up Mozilla’s WebDriver implementation.

This command supports a --webdriver-arg '-vv' argument that enables more detailed logging, as well as --jsdebugger for opening the Browser Toolbox.

A particularly useful trick is to combine this with the headless mode for Firefox we learned about earlier:

% MOZ_HEADLESS=1 ./mach wpt --webdriver-arg '-vv' testing/web-platform/tests/webdriver

Harness tests

The Marionette harness Python package has a set of mock-styled unit tests that uses the pytest framework. The following command will run all tests:

% ./mach python-test testing/marionette

To run a specific test specify the full path to the module:

% ./mach python-test testing/marionette/harness/marionette_harness/tests/harness_unit/test_serve.py

One-click loaners

Additionally, for debugging hard-to-reproduce test failures in CI, one-click loaners from <Taskcluster.html> can be particularly useful.

Out-of-tree testing

All the above examples show tests running in-tree, with a local checkout of central and a local build of Firefox. It is also possibly to run the Marionette tests without a local build and with a downloaded test archive from <Taskcluster.html>.

If you want to run tests from a downloaded test archive, you will need to download the target.common.tests.zip artifact attached to Treeherder build jobs B for your system. Extract the archive and set up the Python Marionette client and harness by executing the following command in a virtual environment:

% pip install -r config/marionette_requirements.txt

The tests can then be found under marionette/tests/testing/marionette/harness/marionette_harness/tests and can be executed with the command marionette. It supports the same options as described above for mach.