Review of Firefox desktop automation work – Q1 2016

Today is the last day of Q1 2016 which means time to review what I have done during all those last weeks. When I checked my status reports it’s kinda lot, so I will shorten it a bit and only talk about the really important changes.

Build System / Mozharness

After I had to dig into mozharness to get support for Firefox UI Tests during last quarter I have seen that more work had to be done to fully support tests which utilize Nightly or Release builds of Firefox.

The most challenging work for me (because I never did a build system patch so far) was indeed prefixing the test_packages.json file which gets uploaded next to any nightly build to This work was necessary because without the prefix the file was always overwritten by later build uploads. Means when trying to get the test archives for OS X and Linux always the Windows ones were returned. Due to binary incompatibilities between those platforms this situation caused complete bustage. No-one noticed that until now because any other testsuite is run on a checkin basis and doesn’t have to rely on the nightly build folders on For Taskcluster this wasn’t a problem.

In regards of firefox-ui-tests I was finally able to get a test task added to Taskcluster which will execute our firefox-ui-tests for each check-in and this in e10s and non-e10s mode. Due to current Taskcluster limitations this only runs for Linux64 debug, but that already helps a lot and I hope that we can increase platform coverage soon. If you are interested in the results you can have a look at Treeherder.

Other Mozharness specific changes are the following ones:

  • Fix to always copy the log files to the upload folder even in case of early aborts, e.g. failed downloads (bug 1230150)
  • Refactoring of download_unzip() method to allow support of ZipFile and TarFile instead of external commands (bug 1237706)
  • Removing hard requirement for the –symbols-url parameter to let mozcrash analyze the crash. This was possible because the minidump_stackwalk binary can automatically detect the appropriate symbols for nightly and release builds (bug 1243684)

Firefox UI Tests

The biggest change for us this quarter was the move of the Firefox UI tests from our external Github repository to mozilla-central. It means that our test code including the harness and Firefox Puppeteer is in sync with changes to Firefox now and regressions caused by ui changes should be very seldom. And with the Taskcluster task as mentioned above it’s even easier to spot those regressors on mozilla-inbound.

The move itself was easy but keeping backward compatibility with mozmill-ci and other Firefox branches down to mozilla-esr38 was a lot of work. To achieve that I first had to convert all three different modules (harness, puppeteer, tests) to individual Python packages. Those got landed for Firefox 46.0 on mozilla-central and then backported to Firefox 45.0 which also became our new ESR release. Due to backport complexity for older branches I decided to not land packages for Firefox 44.0, 43.0, and 38ESR. Instead those branches got smaller updates for the harness so that they had full support for our latest mozharness script on mozilla-central. Yes, in case you wonder all branches used mozharness from mozilla-central at this time. It was easier to do, and I finally switched to branch specific mozharness scripts later in mozmill-ci once Firefox 45.0 and its ESR release were out.

Adding mach support for Firefox UI Tests on mozilla-central was the next step to assist in running our tests. Required arguments from before are now magically selected by mach, and that allowed me to remove the firefox-ui-test dependency on firefox_harness, which was always a thorn in our eyes. As final result I was even able to completely remove the firefox-ui-test package, so that we are now free in moving our tests to any place in the tree!

In case you want to know more about our tests please check out our new documentation on MDN which can be found here:

Mozmill CI

Lots of changes have been done to this project to accommodate the Jenkins jobs to all the Firefox UI Tests modifications. Especially that I needed a generic solution which works for all existing Firefox versions. The first real task was to no longer use the firefox-ui-tests Github repository to grab the tests from, but instead let mozharness download the appropriate test package as produced and uploaded with builds to

It was all fine immediately for en-US builds given that the location of the test_packages.json file is distributed along with the Mozilla Pulse build notification. But it’s not the case for l10n builds and funsize update notifications. For those we have to utilize mozdownload to fetch the correct URL based on the version, platform, and build id. So all fine. A special situation came up for update tests which actually use two different Firefox builds. If we get the tests for the pre build, how can we magically switch the tests for the target version? Given that there is no easy way I decided to always use the tests from the target version, and in case of UI changes we have to keep backward compatibility code in our tests and Firefox Puppeteer. This is maybe the most ideal solution for us.

Another issue I had to solve with test packages was with release candidate builds. For those builds Release Engineering is not uploading nor creating any test archive. So a connection had to be made between candidate builds and CI (tinderbox) builds. As turned out the two properties which helped here are the revision and the branch. With them I at least know the changeset of the mozilla-beta, mozilla-release, and mozilla-esr* branches as used to trigger the release build process. But sadly that’s only a tag and no builds nor tests are getting created. Means something more is necessary. After some investigation I found out that Treeherder and its Rest API can be of help. Using the known tag and walking back the parents until Treeherder reports a successful build for the given platform, allowed me to retrieve the next possible revision to be used with mozdownload to retrieve the test_packages.json URL. I know its not perfect but satisfies us enough for now.

Then the release promotion project as worked on by the Release Engineering team was close to be activated. I heard a couple of days before, that Firefox 46.0b1 will be the first candidate to get it tested on. It gave me basically no time for testing at all. Thanks to all the support from Rail Aliiev I was able to get the new Mozilla Pulse listener created to handle appropriate release promotion build notifications. Given that with release promotion we create the candidates based on a signed off CI build we already have a valid revision to be used with mozdownload to retrieve the test_packages.json file – so no need for the above mentioned Treeherder traversal code. \o/ Once all has been implemented Firefox 46.0b3 was the first beta release for which we were able to process the release promotion notifications.

At the same time with release promotion news I also got informed by Robert Kaiser that the ondemand update jobs as performed with Mozmill do not work anymore. As turned out a change in the JS engine caused the bustage for Firefox 46.0b1. Given that Mozmill is dead I was not going to update it again. Instead I converted the ondemand update jobs to make use of Firefox-UI-Tests. This went pretty well, also because we were running those tests already for a while on mozilla-central and mozilla-aurora for nightly builds. As result we were able to run update jobs a day later for Firefox 46.0b1 and noticed that nearly all locales on Windows were busted, so only en-US got finally shipped. Not sure if that would have been that visible with Mozmill.

Last but not least I also removed the workaround which let all test jobs use the mozharness script from mozilla-central. It’s simply not necessary anymore given that all required features in mozharness are part of ESR45 now.

What’s next

I already have plans what’s next. But given that I will be away from work for a full month now, I will have to revisit those once I’m back in May. I promise that I will also blog about them around that time.