Unit tests verify a “unit”, or the smallest piece of an application which is able to be tested. Unit tests are typically used to isolate an individual class or piece of code and write tests against only its functionality.
Unit testing has many advantages, it is:
Unit tests are created for each step of Zurmos development, while writing these unit tests does slow development process a little, it ultimately means that future development and troubleshooting becomes much easier since these tests can be run and problems identified. This also means that developers can be confident that their systems built on Zurmo are upgrade safe.
For more on unit testing please see this tutorial Running Unit Tests – Explained