The unit testing framework is part of Visual Studio (and not the .NET Framework itself). Unit testing in Visual Studio includes a set of framework classes, the tools, and the execution host. You can find the namespace that contains the unit testing framework classes at
Microsoft.VisualStudio.TestTools.UnitTesting. Developers are most interested in the attribute classes and the
Assert class in this namespace. This section highlights the core usage scenarios for both the attribute and the assertion classes (among others).
The namespace for unit testing is
Microsoft.VisualStudio.TestTools.UnitTesting. However, you set a reference to the assembly