Several leak failures have slipped passed continuous integration
ahalberstadt at mozilla.com
Thu Dec 29 16:37:15 UTC 2016
Over the holidays, we noticed that leaks in mochitest and reftest were
not turning jobs orange, and that the test harnesses had been running in
that state for quite some time. During this time several leak related
test failures have landed, which can be tracked with this dependency tree:
The issue causing jobs to remain green has been fixed, however the known
leak regressions had to be whitelisted to allow this fix to land. So
while future leak regressions will properly fail, the existing ones (in
the dependency tree) still need to be fixed. For mochitest, the
whitelist can be found here:
Other than that, leak checking is only disabled on linux crashtests.
Please take a quick look to see if there is a leak in a component for
which you could help out. I will continue to help with triage and
bisection for the remaining issues until they are all fixed. Also big
thanks to all the people who are currently working on a fix or have
already landed a fix.
Read on only if you are interested in the details.
_Why wasn't this caught earlier?
The short answer to this question is that we do not have adequate
testing of our CI.
_The problem happened at the intersection between mozharness and the
test harnesses. Basically a change in mozharness exposed a latent bug in
the test harnesses, and was able to land because it appeared as if
nothing went wrong. Catching errors like this is tricky because regular
unit tests would not have detected it either. It requires integration
tests of the CI system as a whole (spanning test harnesses, mozharness
_How will we prevent this in the future?_
Historically, integration testing our test harnesses has been a hard
problem. However with recent work in taskcluster, python tests and some
refactoring on the build frontend, I believe there is a path forward
that will allow us to stand up this kind of test. I will commit some of
my time to fix this and hope to have /something/ running that would have
caught this by the end of Q1.
I would also like to stand up a test harness designed to test command
line applications in CI, which would provide another avenue for writing
test harness unit and integration tests. Bug 1311991
<https://bugzilla.mozilla.org/show_bug.cgi?id=1311991> will track this work.
It is important that developers are able to trust our tests, and when
bugs like this happen, that trust is eroded. For that I'd like to
apologize, and express my hope that this will be the last time a major
test result bug like this happens again. At the very least, we need to
have the capability of adding a regression test when a bug like this
happens in the future.
Thanks for your help and understanding.
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