Allow ResourceTestBase methods to be used without the rest of the base class

This was a bit of a pain, these test classes are massive (hence why they're so slow...), but it's one of the very last tests that wraps around all the other tests in a job.

Large MR, but moving the methods around didn't seem to break anything. Could we get a change record for the move though? Can imagine it's something contrib modules could benefit from

Added a CR.

looks like it could use a manual rebase.

Thanks LGTM!

Diff no longer applies.

Rebased.

Ugh rebase seemed to break a few tests.