We already mentioned that we, as professionals, will not ship anything without first determining that it works. Throwing something over the wall to QA, to our users, or to the general public and hoping that it all works as expected just isn't how we do business. We will verify that our code and our applications work as expected. In the beginning, while the application is small and has little functionality, we can manually test everything we can think of. But, as the application grows in size and complexity, it just isn't feasible for developers or anyone else to manually test an entire application. It’s too time-consuming and costly to do this manually. We can save ourselves time and our clients and companies money by automating our testing. We can do so quite easily, from the beginning, through TDD.