Use STDIN project in test_projects to ensure it runs quickly (#2575)
Use STDIN project in test_projects to ensure it runs quickly (#2575)

Existing test was actually running a full black-primer
run which could be slow. This goes from 8 seconds to
0.4 seconds on my machine.

Needed to move to top level scope to leverage the caplog
feature of pytest in order to test that the command line
was parsing the bogus arguments and dumping to stderr.
psf/black