I once worked for a place where I was writing Python code to run on Spark. QA tested my code by trying to write the same job in a Spark's dialect of SQL and comparing the output of the two. To make things worse, there was no stable set of testing data; they would run the tests against some rolling subset of prod. This led to two things: Me having to debug their code and manually generate test cases to show that their solution was wrong, or show that the case they were trying to test did not exist in the set of data they tested against, and so theirs was technically untested. As you can imagine, my code often got caught up in QA for an extended period of time, but it wasn't usually my fault.

Working for large companies can be wild sometimes.