How test harnesses work
python runner the python runner: sets up the testing environment sets up environment variables (mozrunner, currently) creates a profile (mozprofile via mozrunner) sets appropriate test preferences inserts a shim extension in the profile (for non-marionette tests) gathers the tests (manifestdestiny) potentially sets up an http server for test data (mozhttpd) invokes the binary (mozrunner) it is the job of the shim extension to shut down the browser logging (mozlog, in theory) (run tests, accrue results) cleanup: shutdown the browser check for crashes (mozcrash) reporting (moztest) marionette tests list of testing extensions pageloader (talos) mochites...