Not really, testing the changes is rather simplistic. There'd be a debug mode in the game for development. This can range from something as complex as floating damage markers like RPGs use or a few lines in the GUI all the way to a simple log that gets output and read after the fact. The code for weapon damage works, balancing them is just quite literally changing numbers. Sure, it may be a lot of trial and error but it's not complicated and not anywhere near as time consuming as adding in an entirely new network feature.

It's easy but takes a long time. Checking if a payment was successfully is just checking it works, checking if everything is balanced is a longer process. Seen plenty of games where they boost a stay (in this example magic attack) didn't fully test it and mate became the meta.

That implies bungie tested the OP pulse rifles we have now which means either they don't test shit or they're ok with imbalanced guns Either way, it's shit