Error:does not contain a definition for '' and no extension method

If you want to test AHPModel class which is in another project, then you can add a reference to that project (http://msdn.microsoft.com/en-us/library/wkze6zky.aspx). The class and members must be accessible, i.e. public.

Since you are using NUnit, then also consult the corresponding documentation and samples.

Visual Studio includes tools for Unit Testing: http://msdn.microsoft.com/en-us/library/dd264975.aspx, http://www.microsoftvirtualacademy.com/training-courses/software-testing-with-visual-studio-2012-exam-70-497-jump-start?mtag=MVP4000065