[prateekdayal]

I would argue that TDD makes you think more about the design of your system. Also, it makes it easier for you to refactor (as you don't worry too much about accidentally breaking something) and hence keep the code quality high over time

[kerkeslager]

In addition to making you think more about your design, I'd say it makes your design inherently more flexible. Once your design is flexible enough to do two different things, it's much more likely to be able to do three things than if it could only do one thing. And when you do TDD, your design is always capable of two things: fulfilling the requirements and testing.