Make test_file.py tests parallelizable

[Peque]

Just a small change that makes tests in test_file.py parallelizable. This is useful for being able to run tests in parallel with pytest (i.e.: pytest -n 8).

Note that pytest-xdist module is required in order to use the -n option with pytest.

[mmckerns]

This file takes little to no time to run as is. Your point is that with these changes, all the tests can run in parallel?

[Peque]

@mmckerns That is exactly my point, yes. 😊

[matsjoyce]

Futureproofing!

[mmckerns]

This change is fine, in general. I'd rather not have a print in clean_artifact. It seems unnecessary, can you remove it?

[Peque]

@mmckerns Removed unnecessary print.