I rewrote the backend on a team I used to work on. The service had a ton of unit tests. Given that this was a full rewrite, those unit test were useless. I spent the first few days writing a comprehensive suite of integration tests I could run against the existing service. These tests directly mimicked client calls, so the same tests should be just as valid for the rewritten service. Using these tests, I was able to catch 90%+ of potential issues before cutting over to the new service.
Personally, I find unit tests to be mostly useless. Every time I touch code with a unit test, I also need to change the unit test. Rather than testing, it feels like writing the same code twice.
Personally, I find unit tests to be mostly useless. Every time I touch code with a unit test, I also need to change the unit test. Rather than testing, it feels like writing the same code twice.