Debugging a website in an efficient way is one of the most important jobs of PHP developers. These days, a website is a lot more than a few simple HTML pages. In a Magento store, you have a lot of complex business logic that is used in the flow of an e-commerce transaction.
Debugging in PHP is not out of the box like in other programming languages, such as .NET and Java. There are many ways to configure a PHP debugger (such as Xdebug). With a good code editor and debugger, debugging in Magento is much easier.
Another part of debugging and code testing are automated tests. Automated tests, or Unit tests, are developed to test the output of functions for a given input. When some code is changed, you can run the tests and a report will be generated about the failed and passed tests.