I am experiencing the same but when I run the setup on my local machine the test runs fine and the actual output includes ["", “”, “”] the empty items too. Maybe this is a version error or something?
Updated:
Turns out it indeed was version error. Update the poetry.lock Matplotlib package to install version “3.1.3” instead of “3.3.0” and program worked passing the test.
Apparently the updated version of the matplotlib does not read empty string as text?