> What happens next week when someone does an x += hugeBlockOfText in a loop?
Then it will show up in your profiling? If you're doing something perf-critical it is absolutely insane not to be running it through a profiler suite on a regular basis. Your continuous integration system can (or should) be completely capable of replaying real or synthetic activity in order to demonstrate real-world hotspots.
Tests only find what you already want to find. Performance concerns are much fuzzier than that (unless you want to be writing "performance tests" for literally-literally everything, which you're welcome to do but I have better things to do than that).
Then it will show up in your profiling? If you're doing something perf-critical it is absolutely insane not to be running it through a profiler suite on a regular basis. Your continuous integration system can (or should) be completely capable of replaying real or synthetic activity in order to demonstrate real-world hotspots.
Tests only find what you already want to find. Performance concerns are much fuzzier than that (unless you want to be writing "performance tests" for literally-literally everything, which you're welcome to do but I have better things to do than that).