> For one thing, I think resources could be implemented in terms of skips

While working on #17333 I noticed a related problem.  Most of the tests in test_imaplib are skipped if the 'network' resource is not specified.  The test contains the following lines to enable those tests when the file is executed directly:

if __name__ == "__main__":
    support.use_resources = ['network']
    unittest.main()

but this clearly doesn't work while using unittest discovery, so those tests are skipped.

Implementing resources as skips makes sense, but we might also need a way to specify what resources are needed that works with unittest discovery.  Running these tests only when the test file is executed directly or through `regrtest -u` is also an option.