MVC - Unit Testing - Fix errors - The type or namespace name 'ViewResult' could not be found (are you missing a using directive or an assembly reference?)

Errors
The type 'System.Web.Mvc.ActionResult' is defined in an assembly that is not referenced.

The type 'System.Web.Mvc.Controlleris defined in an assembly that is not referenced.

The type or namespace name 'ViewResult' could not be found (are you missing a using directive or an assembly reference?)

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To fix it add the following reference: System.Web.Mvc and the following using: System.Web.Mvc