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).
Axocover Vs Opencover
Go to the directory where AxoCover is installed. You can locate this by running a long test (e.g. Thread sleep, and open the file location of the AxoCover.Host-.exe from the task manager. For example for me it is: C: Users venkat AppData Local Microsoft VisualStudio 15.06d93d79f Extensions pfu3q5ow.kny. AxoCover: VSColorOutput: Repository: 240 Stars: 357 27 Watchers: 25 57 Forks: 79 49 days Release Cycle: 54 days over 1 year ago: Latest Version: 12 months ago. Comment the next line if you want to. Cache can be ignored. Backup files are not needed.
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.
Vs Code Xunit
Still lot to explore, but definitely worth trying it !!