Visual Studio has in-built support for code coverage for Enterprise Editions only. For other editions – you have option to use paid/licensed tools like dotCover.
If you are looking for something free/opensource – OpenCover is very good code coverage tool. But to work with it in Visual Studio, you can use it with some other tool e.g. ReportGenerator. See how to do it here. (VS extension is – OpenCover UI).
But there is one more tool – AxoCover which uses OpenCover and integrates nicely with visual studio for for code coverage. Some information can be found here.
Still lot to explore, but definitely worth trying it !!
Learning never exhausts the mind !! 