In bug 1023423, the following is interspersed is the test's log output: { 08:21:04 INFO - 1402413664376 Browser.Experiments.Experiments TRACE Experiments #0::enabled=true, true 08:21:04 INFO - 1402413664377 Browser.Experiments.Experiments TRACE Experiments #0::Registering instance with Addon Manager. 08:21:04 INFO - 1402413664377 Browser.Experiments.Experiments TRACE Experiments #0::Registering previous experiment add-on provider. 08:21:04 INFO - 1402413664378 Browser.Experiments.Experiments TRACE PreviousExperimentProvider #0::startup() 08:21:04 INFO - 1402413664378 Browser.Experiments.Experiments TRACE Experiments #0::_loadFromCache 08:21:04 INFO - 1402413664383 Browser.Experiments.Experiments TRACE Experiments #0::_loadTask finished ok 08:21:04 INFO - 1402413664383 Browser.Experiments.Experiments TRACE Experiments #0::_run 08:21:04 INFO - 1402413664384 Browser.Experiments.Experiments TRACE Experiments #0::_main iteration 08:21:04 INFO - 1402413664384 Browser.Experiments.Experiments TRACE Experiments #0::_evaluateExperiments 08:21:04 INFO - 1402413664386 Browser.Experiments.Experiments TRACE Experiments #0::_main finished, scheduling next run } We should set whatever prefs we need to in automation to ensure this doesn't happen outside of when we are testing experiments code (similar to what we do for updates, telemetry etc). We'll need to make sure prefs are set for all platforms and all test suites (there are multiple places for all of these prefs sadly). Georg, would you mind taking a look?

Another one in bug 1023809.

We do not want to completely disable the experiment system during tests. We do set the manifest URL to a dummy URI at http://mxr.mozilla.org/mozilla-central/source/testing/profiles/prefs_general.js#61 so that no experiments will actually be activated except in the experiment tests. I think this is WFM.

Indeed, this should be fine and not break other tests. The experiments code is highly async and shouldn't block other operations noticably.

(In reply to Benjamin Smedberg [:bsmedberg] from comment #2) > We do not want to completely disable the experiment system during tests. We > do set the manifest URL to a dummy URI at > http://mxr.mozilla.org/mozilla-central/source/testing/profiles/prefs_general. > js#61 so that no experiments will actually be activated except in the > experiment tests. > > I think this is WFM. Note that that file only applies to mochitests and a few others - for everything else prefs have to be set in additional places (sigh; bug 1023483 comment 0) - and so experiments are in fact being pulled from telemetry-experiment.cdn.mozilla.net during talos runs :-( (see bug 1030093)