Using vsperfmon to get code coverage for a REST service running in IIS

Question

I am trying to get code coverage metrics for an ASP.NET REST service (that uses a global.asax file) running in IIS. I have followed the following basic steps:

1. Set environment variable using "VSPerfClrEnv /globaltraceon" (then reboot computer) (I have also tried /globalsampleon)
2. Instrument the DLLs for code coverage using “vsinstr –coverage ” and I do this for the 5 DLLs I am interested in
3. Start the profiler using "VSPerfCmd /start:coverage /output:cc.coverage /CS /user:Everyone"
4. Start the service in IIS 10 1703, use Task Manager to note the PID for w3wp.exe
5. Attach the profiler to the service using "VSPerfCmd /attach:"
6. Run tests from Visual Studio '17 Enterprise Test Explorer against the service
7. Use "VSPerfCmd /detach"
8. Use "VSPerfCmd /shutdown"

But then when I open the cc.coverage file that was created, only one or two of the DLLs (it's not consistent) have coverage results, and the tests absolutely would have exercised code in all 5 DLLs. Am I doing something wrong or missing a step? Thank you!

Answer 1

According to https://blogs.msdn.microsoft.com/tfssetup/2015/08/13/steps-to-check-the-code-coverage-of-a-web-application-via-command-line/, you should issue a iisreset /STOP command before vsperfcmd /shutdown, after vsperfcmd /detach. Not sure if this is the root cause of your problem or not, but it could be considering that it seems like a buffer flush is not occurring faithfully in your scenario. The buffer flush for each module is required in order to get the coverage data out of the session - if all the things aren't properly shutdown, then this can cause buffers to fail to flush their data.