When I started learning how to write software, the apps I built were really simple. Page hit counter, guestbooks and a way for me to add articles to a blog. None of these required a lot of code to be written.
Over the years the apps that I have written have increased in complexity. Now there are more than 15-20 features to look after, each with its own set of sub features. The front end code base is now as big in size as the backend code base demanding its own set of tests.
Writing tests for your software is good. As your app grows in complexity, it makes it easy to ensure that all the features still continue to work, after the most recent change you made. And if they don’t your tests should tell you that.
I did not part take in Test Driven Development till last year and now that I understand the process(still learning) and its benefits, I would recommend it to everyone who writes software for a living.