Policy suggestion: Use rules_testing for new tests on rules

[matts1]

I notice that we've been using @bazel_skylib's analysis_tests (eg. here).

I've recently been using rules_testing to add a bunch of tests to rules_cc, and I've found the experience to be much better.

Do we want to make a policy that new tests for rules use rules_testing?

[daivinhtran]

I wrote a few tests with rules_testing and agree that it's a much better experience and saves a lot of boilerplate code.

I already introduced it in #2480. @UebelAndre thought it's better idea to convert a few existing tests to get a better sense of the improvements in comparison before we enforce it.

I haven't got the time to do so.

[matts1]

Ah, I didn't notice that, that's awesome!

FWIW, I've been working with it quite a lot recently, and I've found that while it does have some things with it that I take issue with, even with those issues it's still a much better than the alternative.

In general, I'd say that it works very well for simple types, but for more complex types it lacks proper generics (see bazelbuild/rules_testing#93)