Writing Tests with Marionette
Marionette itself is a remote driver, but we have a test runner integrated with our python marionette client that's designed with Marionette in mind. This test runner can run tests according to environment (desktop browser, Fennec on emulator, etc.). For these kinds of tests, you'll need to write Marionette Python tests.
Marionette itself has simpletest-like features to it that will let you run tests within the JS runtime, and will return you the results of the test. Our client uses this capability for the Marionette JavaScript tests, self-contained pure JavaScript tests that can run in either chrome or content.
Types of Tests Supported
The test runner supports Marionette Python tests, which are similar to Selenium tests.
There are also Marionette JavaScript WebAPI tests, which are similar to mochitest-browser-chrome tests.