Fix the pycoast tests further

[mraspaud]

This small PR addresses reviewer comments that where omitted in the last test refactoring PR.

[coveralls]

Coverage: 94.675% (+0.2%) from 94.477% when pulling dedb45c on mraspaud:refactor-pycoast-tests into a37aeec on pytroll:main.

[djhoese]

Looks good and the only uncovered code in that file is now the plotting helper stuff and the saving of an image when the test fails. I see that a failed image is saved to tmp_path. Is that useful since that directory will likely be deleted when the tests finish?

I'll merge this and we can make a new PR if we agree on changes to this.

[pnuu]

I see that a failed image is saved to tmp_path. Is that useful since that directory will likely be deleted when the tests finish?

In my experience the tmp_path stuff is not deleted after the tests run. For example in pytroll/satpy#2316 (comment) there were 3 consecutive runs that were kept within the temp directory. I didn't yet comment there, but as Martin suggested, the next run finally removed the first one (index 0) and created a new entry.

[djhoese]

Ok so we probably still need a print out of the temporary directory on failure so we can easily get to the image.

[mraspaud]

from https://docs.pytest.org/en/7.1.x/reference/reference.html#pytest.tmpdir.tmp_path :

By default, a new base temporary directory is created each test session, and old bases are removed after 3 sessions, to aid in debugging. If --basetemp is used then it is cleared each session. See The default base temporary directory.

[mraspaud]

so 3 runs are kept.
We can of course print the path, but I think it's pretty easy to find, the /tmp/pytest... structure is clear I think.