To even write unit tests effectively you need to write your code in a certain differently.

In C# this normally means using IOC + DI.

Also almost nobody I know does proper TDD. I know it is very convincing when one of the TDD evangelists shows you how to write something like a method to work out the nth number in a fibonacci sequence using nothing but just writing tests.

In reality most 95% of developers that even write tests write the logic and write the test afterwards to check the logic does what it should.