[testing] Add unit tests to scripts

[brylie]

None of the scripts appear to have unit tests. It might be worthwhile to choose a unit testing strategy and start adding basic tests to the scripts. This might entail some re-factoring, abstraction, and possibly merging of similar scripts (e.g. the point/line routing scripts).

[anitagraser]

I'm trying to get unit tests working (see 977ba00) but I'm having trouble making Processing find the user scripts.

I always get Error: Algorithm not found.