Perhaps look into unit testing?
I went searching for a unit testing framework a while back and decided that I wanted to wait until C++17 was closer to release and more supported. Because macros 👎 and C++17 adds a couple features that i think should allow unit testing frameworks to nolonger use macros...
I'll have to take another look though the various frameworks since its been probably a year since i last took a look at the options.
The Google unit testing library seems cool.
I've looked at it but I didn't really like it. There is also catch https://github.com/philsquared/Catch
And another https://github.com/martinmoene/lest
Yet another https://github.com/jimporter/mettle
And I think this is probably the last one I've found for now haha https://github.com/joakimkarlsson/bandit
After thinking about this for a while not everything is easily testable. This is the current stuff that i see to be able to be well tested.
SmfParser parseutils audio(if we had a null output or a raw output or something) stringUtils timing VFS The event dispatcher.