Использование RhinoMocks:
var httpContext = MockRepository.GenerateMock<HttpContextBase>();
var httpRequest = MockRepository.GenerateMock<HttpRequestBase>();
httpContext.Expect( c => c.Request ).Return( httpRequest ).Repeat.Any();
... set up expectations on request...
var controller = new MyController();
controller.ControllerContext = new ControllerContext( httpContext,
new RouteData(),
controller );
...invoke action, check assertions...
httpContext.VerifyAllExpectations();
httpRequest.VerifyAllExpectations();