Unit testing is the first logical phase of testing each building block of an application individually. More important than the testing itself is the ability to develop a Unit Test Case that can be used to test your specific unit of code when needed.

Platform tools like nUnit (C#.NET) and jUnit (Java) enable you to build the Unit Testing (Driver) Classes into your code so that when the application is being tested as a whole, each unit test case can be covered to ensure that all the bits and pieces that make up the process flow are working as intended.

This approach also readily integrates with automated testing initiatives, greatly reducing rework for test automation.