The road to wisdom? — Well, it's plain and simple to express: Err and err and err again but less and less and less. –Piet Hein

Not Testing a Firefox Build (Generic Tasks in TaskCluster)

A few months ago I wrote about my tentative setup of a TaskCluster task that was neither a build nor a test. Since then, gps has implemented “generic” in-tree tasks so I adapted my initial work to take advantage of that.

Triggered by file changes

All along I wanted to run some in-tree tests without having them wait around for a Firefox build or any other dependencies they don’t need. So I originally implemented this task as a “build” so that it would get scheduled for every incoming changeset in Mozilla’s repositories.

But forget “builds”, forget “tests” — now there’s a third category of tasks that we’ll call “generic” and it’s exactly what I need.

In base_jobs.yml I say, “hey, here’s a new task called marionette-harness — run it whenever there’s a change under (branch)/testing/marionette/harness”. Of course, I can also just trigger the task with try syntax like try: -p linux64_tc -j marionette-harness -u none -t none.

When the task is triggered, a chain of events follows:

For Tasks that Make Sense in a gecko Source Checkout

As you can see, I made the script in the desktop-build docker image execute an arbitrary in-tree JOB_SCRIPT, and I created to run mozharness within a gecko source checkout.

Why not the desktop-test image?

But we can also run arbitrary mozharness scripts thanks to the configuration in the desktop-test docker image! Yes, and all of that configuration is geared toward testing a Firefox binary, which implies downloading tools that my task either doesn’t need or already has access to in the source tree. Now we have a lighter-weight option for executing tests that don’t exercise Firefox.

Why not mach?

In my lazy work-in-progress, I had originally executed the Marionette harness tests via a simple call to mach, yet now I have this crazy chain of shell scripts that leads all the way mozharness. The mach command didn’t disappear — you can run Marionette harness tests with ./mach python-test .... However, mozharness provides clearer control of Python dependencies, appropriate handling of return codes to report test results to Treeherder, and I can write a job-specific script and configuration.