Stop defining a default QUnit.reset

Since we’re deprecating QUnit.reset, we should stop relying on it. We could replicate the behavior almost perfectly by automatically registering a testDone callback that includes the current logic, but executes it only when QUnit.reset === undefined (or even !hasOwn.call(QUnit, "reset")).

I say “almost perfectly” because the current code runs after all testDone callbacks, but this proposal would have it run before them. This seems acceptable to me, but if it’s a problem we can explore a promise-based remedy.

[trentmwillis]

@gibson042 this seems like a reasonable approach to me. I can take a crack at implementing it this weekend, if you don’t get to it by then.

[gibson042]

It seems to me that legacy compatibility motivates us to automatically reset the DOM at test boundaries, even though such functionality is arguably more appropriate in a user-defined callback, e.g. testStart. But it should always be possible to correct the inverted default and prevent QUnit from doing anything. As of 0baf467d56735da6de22c377e991ec799460278a, the only way to do so is by removing #qunit-fixture, which isn’t great. And when we consider the weirdness of a DOM coupling in test.js that is indirectly dependent upon the HTML reporter (for initial definition of QUnit.config.fixture), I think the best approach looks something like the following:

• Initialize QUnit.config.fixture in core instead of the HTML reporter, still waiting for a “begin” event but aborting when hasOwn.call( config, "fixture" ) to avoid overwriting user-provided values (even undefined ones).
• Document QUnit.config.fixture as a public interface, in particular noting that it can be nulled to disable automatic DOM manipulation.
• Skip DOM resets when QUnit.config.fixture == null.
• Throw an exception upon setting of QUnit.reset, since we have at least one example of overwriting it and we don’t want silent failure to invoke it.

This will preserve the legacy behavior of automatic inter-test DOM resets, but provide a documented means by which to control them, and reduce HTML reporter dependence to boot.