[ruby-core:67346] Future of test suites for Ruby

I'll try to be brief so we can discuss all this. tl;dr: RubySpec is
valuable, MRI tests are valuable, we need to better utilize both of
them.

As you may have heard, Brian Shirai officially ended the RubySpec
project last week:
http://rubini.us/2014/12/31/matz-s-ruby-developers-don-t-use-rubyspec/

I believe this is a good opportunity for us to address concerns about
how Ruby behavior is being tested over time.

I think we can agree on the following facts:

* ruby-core devs *have* been using RubySpec on and off, and at least
some of us see value in continuing to do so. naruse already maintains
a fork at github/naruse/rubyspec.

* MRI's suite is not nearly as bad as the post claims. I have done
some coverage measurements that show it doing at least as well as
RubySpec for core classes, and significantly better for standard
libraries.

* MRI's tests are often hard to read, too large, undercommented.
There's a lot of room for improvement, but this is obviously an
organic codebase that has had many contributors.

* Ugly tests are harder for users (and contributors) to grok. Ugly
tests are less attractive targets for contribution.

* RubySpec represents a valuable set of tests for Ruby behavior. There
will be a large overlap with MRI's tests, but RubySpec does things
that MRI's suite does not (and vice versa).

* RubySpec is not gone; Rubinius will still need a suite to verify
Ruby compatibility. RubySpec lives in the Rubinius repository now.

There's a number of paths forward for us right now.

* Do nothing. Run the last public RubySpec dump periodically to ensure
we don't regress, as has been done with naruse's fork. New tests
continue to go into MRI suite.

This is the status quo, and I don't think anyone benefits from it
other than folks who dislike change.

* Begin an effort to bring missing tests from RubySpec into MRI's
suite and to clean up and improve MRI's suite. Abandon RubySpec at
some point.

I think *some* effort should be made to improve MRI's suite in the
short term, since we obviously aren't going to throw it away. I don't
like the idea of spending a lot of time porting tests one way or the
other...at least until we've picked a winner. I don't like the idea of
abandoning RubySpec, since it has many valuable features.

* Take over RubySpec as a fork and begin to maintain it as a secondary
suite for MRI. Encourage contributors and committers to write specs
rather than tests.

I think this is possible. The barrier to contributing to RubySpec is
much lower if we're maintaining a fork of it, and I think that
eliminates many obstacles. I also feel like the future needs to be in
either RubySpec or a much cleaner version of MRI's suite, and there's
less work to start using the former now.

...

So that's what I have for now. Give me your thoughts...anything goes.