All the time. 300-400k SLOC in C++. Legacy in the sense that there were no tests of any kind. Little-to-no documentation. Solo developer at the tiny company. Fix bugs and add features while keeping the system available to the tens of thousands of users.
A more recent example: here’s a patch for a critical feature we need. It was written over a year ago. The original author isn’t available anymore. You can write the code from scratch or try to resurrect the patch against master.
Being able to jump into a project and lead people towards some goal is definitely a skill for senior developer positions. Yes, you generally have a team you can lean on and have the ability to do research and all that. But how do you show that you can do all that in an interview?
Agree with the conclusion that a good thing to test for is for problem-solving.
The tech side depends a lot on what you’re doing. Although it gets ridiculous and organizations get lazy with this part. You don’t need to be white boarding graph algorithms for a junior web developer role. If your application is a social networking role and you’re interviewing a senior developer or architect? Definitely. They’re going to be teaching this stuff and need to understand it at a deep level.