Implement Unit Tests for existing code

[Benzammour]

We should aim to get our current code base to a coverage above 80% (chosen arbitrarily, based on sonarcloud's default configuration).
To do so we should aim to get our files with 0% coverage to something significantly higher than this.
As of now, these would be:

file	unit tests	PR
cli.c	✅	#35
log.c	✅	#39
rom.c	✅	#40
mmu.c	✅	#41

Something we might have to look into more is

• lcd.c

as this will contain most of our SDL code.
Something interesting may be mocking the user input in order to test various configurations while running headless.
However, I don't know if this is doable in a concise way in C.

Resources:

• CMock