This document provides an introduction to unit testing using Nunit. It discusses what unit testing is, the benefits of unit testing, and what is needed to perform unit testing. It then focuses on Nunit, explaining that Nunit is a unit testing framework for .NET languages. It provides hands-on examples of creating a test project using Nunit to test methods in a BMI calculator application. It demonstrates running tests using both the Nunit graphical user interface and console modes.