Test driven development is great as long as you have proper tests. The problem is that it’s very hard to predict enough edge cases to cover the field of possible scenarios. Code coverage analysis will help developers make sure all code blocks are executed, but it doesn’t do anything to ensure an application correctly handles the variations in data, user interaction, failure scenarios, or how it behaves under different stress conditions.
The fact that tests are helpful, but never complete is something most developers are already conscious of. The danger is that better tests make worse developers! It’s very easy to lean too heavily on passing tests, wildly changing code until the light goes green without spending enough time thinking through the application’s logic.
I’m basically saying that, psychologically speaking, passing tests gives us a false sense of security. They can be a distraction from carefully crafted and thought through code. That’s why I advocate writing tests only for the purposes of regression testing. It should be a follow-up step, not an integral part of initial development.