Yes, this remains an issue. Please see the test project (which I attached
when uploading, but which I no longer have) and notice that play mode tests
aren't fully scene-isolated.
To explain again the issue, when running Play Mode tests that load a scene,
the [TearDown] method for that test gets called before the scene is fully
destroyed. The result is that if objects in the scene change global values
OnDestroy, the TearDown method can't reset them. In fact, it's much worse
than that, since the subsequent test's [SetUp] method actually gets called
before the previous scene's objects' OnDestroy is called. This means that
[SetUp] can't be used to get a clean slate; cruft from a previous test
could still be running even after [SetUp] finishes on the next test.
My hope would be that if you load a scene in a Play Mode test, that scene
will be fully unloaded prior to [TearDown] being called. But it should
*definitely* be the case that the scene should be fully unloaded before
starting the next Play Mode test in a test run.