Sounds great.
I hope this also is plus for C-C TB mochitests as well. :-)
I run them locally and on try-comm-central and often I see intermittent
errors.
Chiaki
On 2025/06/18 0:38, Florian Quèze wrote:
Did you know that until 2 weeks ago, very many browser-chrome
mochitests included 300ms waits?
Whenever `BrowserTestUtils.switchTab` was called (either directly, or
indirectly from helpers like `openNewForegroundTab` or `withNewTab`),
it waited for a `TabSwitchDone` event which is only dispatched after a
300ms delay controlled by the `browser.tabs.remote.unloadDelayMs`
preference.
This wastes time, but even more importantly, it makes the tests fail
intermittently whenever the thing the test should have actually been
waiting for starts taking slightly longer than 300ms. See
https://firefox-source-docs.mozilla.org/testing/intermittent/index.html#using-magical-timeouts-to-cause-delays
for more information about why timers should be avoided in tests.
In https://bugzilla.mozilla.org/show_bug.cgi?id=1702637, I changed
`BrowserTestUtils` to instead wait for the `TabSwitched` event, which
is dispatched immediately after the new foreground tab becomes visible.
Consequences of this change include:
- Many browser-chrome mochitests now run much faster locally.
- The average bc job time on CI has decreased by about a minute.
- A few tests became perma-fail, and many low frequency intermittent
failures became frequent. To green up the tree, I introduced a
“test.wait300msAfterTabSwitch” preference that reverts to the previous
behavior, and I had to set this pref in a bit more than 350 tests
(that’s about 4.5% of all browser chrome mochitests).
Please avoid setting the “test.wait300msAfterTabSwitch” preference in
new tests and instead await the thing the test actually needs.
Debugging existing tests in your components to remove the preference
would also be useful, but I understand that other tasks are higher
priority. Debugging this kind of issue might be a good way to get
familiar with using the Firefox Profiler to debug tests failures
(https://firefox-source-docs.mozilla.org/testing/mochitest-plain/index.html#debug-using-the-firefox-profiler
).
Separately, in https://bugzilla.mozilla.org/show_bug.cgi?id=1968587
Joel Maher removed 1s timers that delayed the execution of other
flavors of mochitests. This should make running these kinds of
mochitests locally much more efficient.
--
Florian Quèze
--
You received this message because you are subscribed to the Google
Groups "dev-platform@mozilla.org" group.
To unsubscribe from this group and stop receiving emails from it, send
an email to dev-platform+unsubscr...@mozilla.org.
To view this discussion visit
https://groups.google.com/a/mozilla.org/d/msgid/dev-platform/CAFu36SrPcP32Uv9yV0jw7pYfjtJTdOBC-Sj_kzxusY_8%2Be-JZg%40mail.gmail.com
<https://groups.google.com/a/mozilla.org/d/msgid/dev-platform/CAFu36SrPcP32Uv9yV0jw7pYfjtJTdOBC-Sj_kzxusY_8%2Be-JZg%40mail.gmail.com?utm_medium=email&utm_source=footer>.
--
You received this message because you are subscribed to the Google Groups
"dev-platform@mozilla.org" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to dev-platform+unsubscr...@mozilla.org.
To view this discussion visit
https://groups.google.com/a/mozilla.org/d/msgid/dev-platform/12ba2e55-9dce-4780-bb93-4f78cf9c2c03%40yk.rim.or.jp.
