Unit tests for all code

[jcpunk]

There really should be unit tests for all the C and shell code to validate compatibility.

I hear https://cmocka.org/ is a good testing framework, but have no real experience with any existing C frameworks.

It looks like https://github.com/sstephenson/bats is the way to go for testing out shell scripts - plus https://github.com/koalaman/shellcheck

Long term plan is to integrate with #2

Open to other ideas!