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# Mn Python tests
_Marionette_ is the codename of a [remote protocol] built in to
Firefox as well as the name of a functional test framework for
automating user interface tests.
The in-tree test framework supports tests written in Python, using
Python’s [unittest] library. Test cases are written as a subclass
of `MarionetteTestCase`, with child tests belonging to instance
methods that have a name starting with `test_`.
You can additionally define [`setUp`] and [`tearDown`] instance
methods to execute code before and after child tests, and
[`setUpClass`]/[`tearDownClass`] for the parent test. When you use
these, it is important to remember calling the `MarionetteTestCase`
superclass’ own [`setUp`]/[`tearDown`] methods since they handle
setup/cleanup of the session.
The test structure is illustrated here:
```python
from marionette_harness import MarionetteTestCase
class TestSomething(MarionetteTestCase):
def setUp(self):
# code to execute before any tests are run
MarionetteTestCase.setUp(self)
def test_foo(self):
# run test for 'foo'
def test_bar(self):
# run test for 'bar'
def tearDown(self):
# code to execute after all tests are run
MarionetteTestCase.tearDown(self)
```
[remote protocol]: Protocol.md
## Test assertions
Assertions are provided courtesy of [unittest]. For example:
```python
from marionette_harness import MarionetteTestCase
class TestSomething(MarionetteTestCase):
def test_foo(self):
self.assertEqual(9, 3 * 3, '3 x 3 should be 9')
self.assertTrue(type(2) == int, '2 should be an integer')
```
## The API
The full API documentation is found [here], but the key objects are:
* `MarionetteTestCase`: a subclass for `unittest.TestCase`
used as a base class for all tests to run.
* {class}`Marionette <marionette_driver.marionette.Marionette>`: client that speaks to Firefox
[here]: /python/marionette_driver.rst
## Registering Test Manifests
To run Marionette Python tests locally via `mach` or as part of the `Mn` tests jobs
in CI they need to be registered. This happens by adding a manifest file to the tree,
which includes a reference to the test files and expectations for results.
Such a manifest file can look like the following and is stored with the extension `.toml`:
```ini
[DEFAULT]
["test_expected_fail.py"]
expected = "fail"
["test_not_on_windows.py"]
skip-if = ["os == 'win'"]
```
The registration of such a manifest file is done in two different ways:
1. To run the tests locally via `./mach test` or `./mach marionette-test` the
created Marionette manifest file needs to be referenced in the folder's related
`moz.build` file by adding it to the `MARIONETTE_MANIFESTS` variable like:
MARIONETTE_MANIFESTS += ["test/marionette/manifest.toml"]
2. To run the tests in CI the manifest file also needs to be included in the
Marionette's own [master manifest file]. This ensures that the test packaging step
will find the tests and include them as well in the test package.