Healthcare.gov is a good example although not legacy codebase. Anyway, I think fixing small bugs and writing tests are best way to learn how to work with legacy

Healthcare.gov is a good example although not legacy codebase. Anyway, I think fixing small bugs and writing tests are best way to learn how to work with legacy system. This allows me to see what components are easier to rewrite/refactor/add more logging and instrumentation. Business cannot wait months before a bug is fixed just for the sake of making a better codebase. But I agree on database changes should be minimal to none as much as possible. Also, overcommunicate with your downstream customers of your legacy system. They may be using your interface in an unexpected manner. I have done a number of serious refactoring myself and god tests will save me a huge favor despite I have to bite teeth for a few days to a few weeks.