With Open-Acidification/TankController#207 our tests went from 42:30 to 2:30! (Unfortunately, we've had to start using a fork of arduino_ci in order to have this work.)

I like what's going on here but I'd feel more comfortable if we found a way to factor this a bit better. For example:

• a constant (or function) instead of a duplicated string to provide the name of the shared library
• a function to calculate the path of the shared library
• a standalone function responsible for building the library
• a standalone function to check whether the shared library exists (if necessary)

I can probably take a crack at this if you'd like

As mentioned a moment ago in another PR, this is the remaining PR that I haven't merged and that is because I'm a bit hesitant, partly for the reasons you suggest (and partly because it doesn't give the speed improvements I anticipated). As long as this is unmerged, our TankController project will continue to use a fork (which is fine; we've been doing it for some months).

So, yes, if you see what I'm trying to do and can find a way to factor it better, that would be wonderful. But, please don't feel an obligation to take my problems and try to solve them!