Unit testing is thoroughly testing the base components that make up an individual feature or function in a website or application. This process is essential for verification of not just the sum, but also the parts in test-driven development.

Unit testing begins by writing a test script for a feature, then the code that defines the desired functionality.

In traditional functional testing, we can only verify the final output, not how we got it. Unit tests paint a much more detailed picture, which allows us to better pinpoint areas of failure and quickly eliminate ares that are working well. Moreover, coding to unit tests ensures that developers are writing in an object oriented way, abstracting their functions into discrete units that can be individually refactored, replaced and improved in the future.

For large scale application development, unit testing and unit based development is a critical framework to ensure that code is always easy to maintain and improve over time.