What is NUnit used for?
the term “unit” refers to code written in .NET that accepts an input, performs certain operations, and returns a result. Unit testing is a method of testing very small bits of code by proving that the unit works correctly given certain inputs.
A lot of unit test frameworks are available for .Net nowadays, if we check in Visual Studio we have MSTest from Microsoft integrated in Visual Studio.
Some 3rd party frameworks are: NUnit MbUnit Out of all these Nunit is the most-used testing Framework.
NUnit is Open Source software and NUnit 3.0 is released under the MIT license. This framework is very easy to work with and has user friendly attributes for working. Learn NUnit from here