Mozilla has a number of source repositories under https://hg.mozilla.org/hgcustom/ that cumulatively define how version control works at Mozilla.

Back in February, I launched an effort to establish a unified Mercurial repository for all this code. That repository is version-control-tools and it has slowly grown.

The latest addition to this repository is the import of the hghooks repository. This now-defunct repository contained all the server-side Mercurial hooks that Mozilla has deployed on hg.mozilla.org.

Soon after that repository was imported into version-control-tools, we started executing the hooks tests as part of the existing test suite in version-control-tools. This means we get continuous integration, code coverage, and the ability to run tests against multiple versions of Mercurial (2.5.4 through 3.1) in one go.

This is new for Mozilla and is a big deal. For the first time, we have a somewhat robust testing environment for Mercurial that is testing things we run in production.

But we still have a long way to go. The ultimate goal is to get everything rolled into the version-control-tools repository and to write tests for everything people rely on. We also want the test environment to look as much like our production environment as possible. Once that's in place, most of the fear and uncertainty around upgrading or changing the server goes away. This will allow Mozilla to move faster and issues like our recent server problems can be diagnosed more quickly (Mercurial has added better logging in newer versions).

If you want to contribute to this effort, please write tests for behavior you rely on. We're now relying on Mercurial's test harness and test types rather than low-level unit tests. This means our tests are now running a Mercurial server and running actual Mercurial commands. The tests thus explicitly verify that client-seen behavior is exactly as you intend. For an example, see the WebIDL hook test.

So what are you waiting for? Find some gaps in code coverage and write some tests today!