Sometimes I look at my co-worker's code and want to vomit. My poor eyes. Also loves to tell me something should work and hasn't tested it...

I have been in that boat way too many times

"Should work" is ONLY applicable if you have rigorously mathematically proven your code to be correct ONLY on a platform that has been rigorously mathematically proven correct from resistor to API level.

Otherwise WRITE FUCKING UNIT TESTS, YOU TOOLS!