Added link to the specific file in question in case someone else is c… (dotnet#9185)

…onfused about the particular file in question, like I was

Author: MarkIannucci

aspnetcore/mvc/controllers/testing.md

@@ -69,7 +69,7 @@ Mocked calls that aren't called are normally ignored, but calling `Verifiable` a
 > [!NOTE]
 > The Moq library used in this sample makes it possible to mix verifiable, or "strict", mocks with non-verifiable mocks (also called "loose" mocks or stubs). Learn more about [customizing Mock behavior with Moq](https://github.com/Moq/moq4/wiki/Quickstart#customizing-mock-behavior).
 
-Another controller in the sample app displays information related to a particular brainstorming session. The controller includes logic to deal with invalid `id` values (there are two `return` scenarios in the following example to cover these scenarios). The final `return` statement returns a new `StormSessionViewModel` to the view:
+[SessionController](https://github.com/aspnet/Docs/blob/master/aspnetcore/mvc/controllers/testing/sample/TestingControllersSample/src/TestingControllersSample/Controllers/SessionController.cs) in the sample app displays information related to a particular brainstorming session. The controller includes logic to deal with invalid `id` values (there are two `return` scenarios in the following example to cover these scenarios). The final `return` statement returns a new `StormSessionViewModel` to the view (*Controllers/SessionController.cs*):
 
 [!code-csharp[](testing/sample/TestingControllersSample/src/TestingControllersSample/Controllers/SessionController.cs?name=snippet_SessionController&highlight=12-16,18-22,31)]