Builds fail intermitently with "FileNotFoundError" (Montserrat-Black.ttf)

[felipesanches]

https://github.com/googlefonts/fontbakery/actions/runs/4075537481/jobs/7022061236

[felipesanches]

A-ha! You know which issue is this one? It's the 4041!

[miguelsousa]

More than one test must be leveraging the same file and they're stepping on each other.

[felipesanches]

Do these tests run in parallel within any given operating system and python version?

[miguelsousa]

The tests are executed independently of each other. They ran in parallel, but there's never more than 8 tests running at any given time (because of this pytest setting).

The fact that the tests are called independently doesn't guarantee that they run in total isolation; if one test happens to be hardcoded to delete file A from location B (for whatever reason) and another test is also hardcoded to do the same, if they happen to run at the same time the likelihood of one of them failing is going to be high. Of course, this isn't a problem if the tests are run sequentially.

[felipesanches]

I think I found the solution!

[miguelsousa]

@felipesanches any progress on the fix. This problem is blocking PRs again. See #4122