How does the testing script work?

I read the linked issue in the README but I'm wondering if I could get a little more detail on how this suite of tests is meant to be used. I looked at the test-rendering.sh script but I could use a little more detail.

I mentioned before of the C++ research project. Right now I don't plan on making any changes to the bodies of any functions; moreso how the code is laid-out/organized. I've already created a python script that can go in and recursively scan this repo for .sif files, have the synfig binary render them out, and then note down how long it took to render each file.

But when looking at some of the code in the main synfig repo I have seen some functions that (that I think) could be rewritten to be more performant. I would like to submit upstream some PRs but I want to make sure I've tested it to make sure I haven't broken anything. Does the test-rendering.sh do A/B testing to verify the output?