Till now I've been testing my web (usually written in PHP) as well as desktop applications (normally Java or C#) manually. Now I read somewhere on the net about automated tests. I tried searching to know about it in details but almost all searches end up at things like PHPUnit. Could someone please put some light on the theory behind automated tests? How a software can be tested automatically? Any limitations etc? Or may be you can tell me a place where I can read about this.
Regards
For testing the correctness of code you can use unit testing. This was first explained to me from Dive Into Python: Unit Testing and will do much more justice to the topic then I could here. Now that you know about the term unit testing, you shouldn't be far from other existing explanations that will make sense to you, be it that one doesn't.
You may find test-driven development of interest too.
Your code is not magically tested for you, as you may had the idea of. The code to test your application will be written by you. What packages like PHPUnit offer you is a framework in which you can implement your tests. These packages will provide many conveniences for defining your tests, running them together as a suite, and generating a report. These are the only automated aspects.