As a developer, the first thing you need to do when you started in a new company or project, is read it’s test suite. If there aren’t tests, or even worse, if you couldn’t wrote a test because of the high code coupling. Prepare for a messy company. There isn’t wrong if that, but the most of your time will be resolving bugs and handle crisis. It’s good for you to develop troubleshooting techniques, but not so good for your career.
In the other hand, if you can understand the rules of the company’s core domain reading the tests, faster you will be valuable for the company, developing new projects, improving your portfolio, and faster you will be a better professional.
Programs must be written for people to read, and only incidentally for machine execute
~Kevlin Henney