Adds edit script unit test

[kylebgorman]

Adapted from:

https://gist.github.com/kylebgorman/0ee3f0f36c386127e96ecf621a345204

Note that this:

• is in classic unittest, whereas I usually use pytest, though the latter is comfortable working with the former.
• is not wired to any CI or commit hook (yet)

I just wanted to add it before I forgot about it.