Add support for unit tests

[oubiwann]

Maybe using this? https://github.com/google/googletest

[oubiwann]

Make examples:

• https://stackoverflow.com/questions/15813723/how-do-i-set-up-google-test-with-a-gnu-make-project
• https://github.com/google/googletest/blob/release-1.8.1/googletest/make/Makefile