Katrina Owen's talk on what she terms "Therapeutic Refactoring" takes a fascinating approach to spaghetti code that arrives without specs or documentation. The answer is so simple it could be mistaken for TDD itself. But "test driven development" doesn't describe how tests fit in here. She's using tests as inquiries. "Hello, codebase. What do you do and what are you expecting?" There's a bit of awe at watching an application reveal itself to a test doing nothing.
Watch the whole thing: Therapeutic Refactoring, by Katrina Owen, Scottish Ruby Conference 2012