Test Driven Development

A simple example: create a UI application (ASP.NET or not) which does nothing above the default project. Then start to write facilities needed for your project. As soon as you create each single method, a single change that cause any manifesting effect, add it to your application, so it could be tested. Test it by yourself or pass to the testing team immediately. (It's the best to combine both ways to test things.) Repeat this cycle until your project is done.

Actually, things are way more complicated than that. There are testing frameworks, you need to do many different kinds of tests, including unit testing, creation of separate prototype covering some parts of technology, testing of your application project during development, regression testing, creation of testing plans and coordination with development plans, and a lot more.

—SA