On 2014-08-09, 10:19 PM, Bobby Holley wrote:
I've mentioned this before [1], but recent checkins in mozilla-central
suggest that this message could use repeating.
Please don't write new tests that do tricky things with SpecialPowers.wrap
and friends (like SpecialPowers.Cc and SpecialPowers.Cu, which do an
implicit .wrap()).
These wrappers are intended to be a quick-and-dirty tool to frob things
from mochitest-plain, but have lots of quirks that cause complicated use
cases to fail in mysterious ways. Moreover, the transitive nature of the
wrappers usually cause them to spread much farther than the author
intended. This can waste a lot of time, and significantly reduces the value
of your tests, because they're testing a complicated/magical/best-effort
proxy layer rather than what we actually ship.
Here are some Do's and Don'ts:
Do:
* Poke various privileged controls (triggered GCs, setting prefs, clearing
caches) to improve the usefulness of a test.
* Examine cross-origin objects to avoid complicated postMessage-based tests.
Don't:
* Import a framework like Task.jsm or Promise.jsm.
* Implement an XPCOM component.
* Interact directly with the JSM backend of a DOM API.
If you find yourself itching to do something complicated, write a
mochitest-chrome test. The default template [2] now generates html files
(rather then XUL files), so the ergonomics there should be easier than
before.
Note that anything tested in mochitest-chrome is not tested on Firefox
OS at all, which is a *great* reason to avoid writing mochitest-chrome
at all costs.
Cheers,
Ehsan
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