Test Explorer continues to show tests as passing even if test modules can no longer be imported

[brettcannon]

I ran my tests and had them passing. Then I moved all of my logic code and broke my imports, but the Test Explorer continued to say my tests were passing. The following is an example of the failures pytest is reporting which are not being reflected in the Test Explorer (the status bar shows the right result):

=================================== ERRORS ====================================
______________ ERROR collecting tests/test_ghutils/test_ping.py _______________
ImportError while importing test module 'c:\Users\brcan\Repositories\pvscbot\tests\test_ghutils\test_ping.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
tests\test_ghutils\test_ping.py:7: in <module>
    from pvscbot.ghutils import ping
E   ModuleNotFoundError: No module named 'pvscbot.ghutils'

[luabud]

Closing in favour of #4586.