Add test for sct_dmri_display_bvecs, then add -v argument to make the test pass

[joshuacwnewton]

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Description

#3091 added loglevel setting steps to all SCT scripts. However, sct_dmri_display_bvecs never had a verbose argument.

This was never caught because there is no test for sct_dmri_display_bvecs. So, this adds an (admittedly very basic) test for the script. (A more thorough test would require some refactoring of sct_dmri_display_bvecs.)

This test fails on master, but passes on this branch after -v is added.

Linked issues

Fixes #3386.

[jcohenadad]

thanks!

[valosekj]

@joshuacwnewton Thanks for incredibly fast workaround. I have just tried your branch and now it works! Thanks!

[joshuacwnewton]

Hrm... the Catalina build has stalled for the past 2.75hr... restarting now. 😅

[joshuacwnewton]

OK, it's still stalling even after a restart. I ran into a similar problem in #3373 with aa23154:

spinalcordtoolbox/unit_testing/cli/test_cli_sct_denoising_onlm.py

Line 10 in aa23154

@pytest.mark.skipif(sys.platform == "darwin", reason="Test hangs on macOS 10.15 CI runners (cause currently unknown)")

Since this is the second time this has happened, I'd like to try and find an explanation...

[joshuacwnewton]

Ah, my hunch is that it has to do with tests that invoke matplotlib.pyplot.show(). Both scripts (sct_denoising_onlm and sct_dmri_display_bvecs) use it, and pyplot is mentioned in our Wiki as causing problems on headless systems.

EDIT: Confirmed by 3b5aefe!