WIP: try to make _test_qunit less horrible to debug

That won't fix the test but at least we'll get a least some debugging output to try to understand what is happening.

Also this code is really weird and only used in QUnitTestCase.test_javascripts. idk if it's used anywhere but it's a public API so I've only made a very small modification but I'm still convinced that this code is weird and not adapted to the current situation.

I'm creating this MR to see how the CI is behaving on this one.