The feature was to parse a set of fairly complex xml files following a legacy schema. Problem was, the way this was done previously did not conform to the schema so it was a guideline at best, which over the course of many years snowballed into an anarchy where clients would send in whatever and it was continuously updated per case as needed. They wanted to start enforcing their new schema while phasing out the old method.

The good news is that parsing and serialization is very testable, so I rounded up what I could find of example files and got to work. Around the same time I asked our client if they had any more examples of typical cases we need to deal with, and sure enough a couple of days later I receive a zip with hundreds of files. They also point out that I should just disregard the entire old set since they decided to outright cut support for it after all if it makes things simpler. Nice.

I finish the feature in a decent amount of time. All my local tests pass, and the CD tests pass when I push my branches. Once we push to our QA env though and the integration tests run, we get a pass rate of less than 10%.

I spend a couple of days trying to figure out what's going on, and eventually narrow it down to some wires being crossed with the new vs. old xml formats. I'm at a loss. I keep trying to chip away at it until I'm left with a minimal example, and I have one of those lean-back moments where you're just "I don't get it". My tests pass locally, but in the QA environment they fail on the same files.

We're now 3 people around my workstation including the system architect, and I'm demonstrating to the others how baffling and black magic this is. I postulate that maybe something is cached in my local environment and it's not actually testing the new files. I even deleted the old ones.

"Are you sure you deleted the right files?"

"Duh of course -- but let me check..."