Improve unit testing

[thatch]

I observed a specific situation where it didn't suggest narrowing:

Variable ['highlighter', 'imperfect', 'LibCST (>=0.3.1)', 'tomlkit (>=0.2.0)', 'pkginfo (>=0.6)']
Fixed []

Versions
========
highlighter ['0.1.0', '0.1.1']
imperfect ['0.0.1', '0.0.2', '0.0.3', '0.1.0', '0.1.1', '0.2.0', '0.3.0']
libcst ['0.3.1', '0.3.2', '0.3.3', '0.3.4', '0.3.5', '0.3.6', '0.3.7', '0.3.8', '0.3.9', '0.3.10', '0.3.11', '0.3.12']
tomlkit ['0.2.0', '0.3.0', '0.4.0', '0.4.1', '0.4.2', '0.4.3', '0.4.4', '0.4.5', '0.4.6', '0.5.0', '0.5.1', '0.5.2', '0.5.3', '0.5.4', '0.5.5', '0.5.6', '0.5.7', '0.5.8', '0.5.9', '0.5.10', '0.5.11', '0.6.0', '0.7.0']
pkginfo ['0.6', '0.7', '0.8', '0.9', '0.9.1', '1.0', '1.1', '1.2', '1.2.1', '1.3.0', '1.3.1', '1.3.2', '1.4.0', '1.4.1', '1.4.2', '1.5.0', '1.5.0.1']
...
FAIL highlighter:0.1.0: Test failed
...
Final test
==========
{'imperfect': <Version('0.0.1')>, 'libcst': <Version('0.3.1')>, 'tomlkit': <Version('0.2.0')>, 'pkginfo': <Version('0.6')>}
OK   min
Everything is fine.