As an android dev when I inherited a shitty project thats when I realized what really means to write readable and most importantly testable code. Codebase I inherited wasnt even really that bad it was quite readable, but boy it was not suited for any unit/instrumented tests. im talking spaghetti code.

Nowadays I refactor apps to make sure they are testable instead of spending weeks writing tests for a shitty codebase which was done without thinking about separation of concerns. Clients hate the extra couple weeks on top of request but what can I do, if they want tests they need to work with TDD approach or give extra time for refactors.