Introduce TestRun objects and refactor TestDatabase to be testable

I've stared at this issue lots of times and little bits of it make me feel "are we sure that we need to do this or that" - for example I'm not sure about the utility of having an interface for TestRunResultsStorageInterface - I get that internally we're going to swap it for a non-simpletest labelled implementation at some point in the future but it feel unnecessary. That said, I'm not sure that these objections are that important or should stand in the way of progress here. I don't think we should consider any of this public API and the MR helpfully adds @internal in quite a few places. Therefore I think we should proceed here with a commit.

Committed f711435 and pushed to 10.1.x. Thanks!

mondrake → closed merge request !192

Thanks. BTW, there's a bit of Space Oddity in Drupal's code, now :)

Automatically closed - issue fixed for 2 weeks with no activity.