setTimeout is not bad because it is async, it is bad because it is non deteministic, async tests can and are reliable. Mochitests are some of the most stable on tbpl and heavily use async api's, just never expect that an action can be done given an arbitrary timeout, have a way for being notified or determining that the action is complete
On 18 December 2013 16:31, Julien Wajsberg <[email protected]> wrote: > Le 17/12/2013 14:06, Dale Harvey a écrit : > > Investigating some unit test failures I am seeing a lot of setTimeout's > > located inside the tests, someone already made a meme for me for the > > occasion > > > > > http://mozillamemes.tumblr.com/post/24322890551/now-if-you-add-an-event-listener-that-sets-a > > > > More specifically everyone is gonna have a bad time because we will have > > buggy intermittent tests and closed trees, just a reminder for coders and > > more specifically reviewers that setTimeouts should pretty much only be > > used to yield / spin the event loop inside tests, not for any form of > timer > > / waiting solution > > > > > What I learnt for 1 year is that setTimeout should _never_ be used in > tests. > Tests should _never_ be asynchronous. If you use setTimeout in code, > then use sinon's fake timers to linearize this code and make it > synchronous. > > I recently rewrote the tests for system's keyboard manager in [1] (still > pending review, wink wink) and the previous tests used another bad > pattern: it injected CSS containing transformations and transitions so > that the code got the "transitionend" events. This is much like > setTimeout: waiting that something asynchronous is happening. I rewrote > this by sending the transitionend event in the test itself, which > reliably triggers the event in a synchronous way, and make it way faster > in the same time. > > The only situation where an asynchronous test was needed was testing > indexedDB code. I don't think we want to mock the indexedDB code to make > it synchronous here. I could still change my mind though ;) So we > increased mocha's timeout a lot, and we expect to have some rare > intermittent with this code. > > [1] https://bugzilla.mozilla.org/show_bug.cgi?id=936369 > > -- > Julien > > _______________________________________________ dev-b2g mailing list [email protected] https://lists.mozilla.org/listinfo/dev-b2g
