On Wed, Nov 4, 2015 at 5:14 PM, James Graham <ja...@hoppipolla.co.uk> wrote:

> On 03/11/15 22:08, Robert O'Callahan wrote:
>
> Why not create a Mochitest compatibility layer over testharness.js so
>> that tests that only use SimpleTest.waitForExplicitFinish(),
>> SimpleTest.finish(), is(), todo() and ok() can run on Servo with trivial
>> changes?
>>
>
> A few reasons I am skeptical of this:
>
> * Mochitests test gecko behaviour, not standardised behaviour. These can
> and do differ. Therefore they are even less trustworthy than the average
> test.
>

I'm not sure what you mean by this. It's easy to write web-platform-tests
that depend on non-standard behavior. I had to debug one such last week.
Furthermore Gecko mochitests have been tested against Gecko, which has
itself been tested on the Web, so Gecko mochitests are far more likely to
be "correct" than a test someone just wrote and only tested on, say, Servo.

* Mochitests are really written assuming the full gecko featureset. Given
> the total lack of isolation between asserts, they may behave rather
> unexpectedly and misleadingly in a browser not having all those features.
>

Many use Gecko-specific features but many don't.

* In the long term having multiple APIs for writing tests that people have
> to learn in order to read tests is a big net negative. If we allow
> mochitests to be upstreamed with a shim we should expect other vendors to
> do the same, and to end up with half a dozen possible test formats.
>

That's fair, though it's a problem we introduced when we started adding
web-platform-tests to the tree.

Put it this way: when Servo needs tests for a feature, I expect it makes
much more sense to take Gecko mochitests for the feature and convert them
to web-platform-tests than to write new tests from scratch.

Rob
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