any developer worth their salt will confirm that unit testing only catches the least offender bugs - the worst offender bugs are those you cant catch just by testing that the function works as intended.
testing that the unit works as intended is usually the first task, after that i test a punch of odd values of different types to see how it reacts. i tend to add error handling very early on in each unit so that only the right values can be passed on to it, and i also assert all inputs when possible.
a lot of my code is in general pretty sloppy and violates every encapsulation/black box rule imaginable, but thats mainly because i'm learning C# from the ground up as i design my game, so everything is implemented rather lazily and brute-forcey but i plan to clean up everything once i have a good prototype
that said, considering it seems to be a small game, you may be able to get away with it. its just a warning i suppose. dont be surprised if it takes a lot longer to finish all the art and sound assets or if people dont like you left out feature x or tutorial y cause you skipped making it out of reducing complexity
yeah the art and sound i expect to take a while but i really plan to cut corners on a lot of stuff (using images instead of facial expression animation, recycling old blockland-intended models as weapons and refurbishing them, stealing melodies from my unused trap beats to use in the game instead, etc). this is the part i'm really excited for because i feel im a better modeler than i am a programmer, and im looking forward to the challenge of trying to make a nice looking game with my very low poly ugly modeling style
if i move past the first prototype and decide to kickstart it and it ends up being successful i can definitely change the scope to match the budget, but my main goal is to figure out a steamlining process for game design so i can make better finished products quicker / also so i can manage seemingly high-budget projects on a low / nonexistent budget, cuz obviously im expecting to make like 3-4 unprofitable games before i come out with something fun and worth some money
