To create unit test project, go to add new projects-> visual C#->Test->Unit Test Project
Now go to Manage Nuget Package->Online->search for "nunit"
Now click on nunit and nunit adaptor
Install both
Now check all references will be added in the aaplication.
Go to the class for unit testing in this added project, where you will get "TestClass".
Add some code in the "TestMethod" function to test.
Go to "Test" menu->Windows->Test explorer
Build code
Select test method in the Test explorer and right click
debug/run the test