AltCover and ReportGenerator give amazing code coverage on .NET Core
I'm continuing to explore testing and code coverage on open source .NET Core. Earlier this week I checked out coverlet. There is also the venerable OpenCover and there's some cool work being done to get OpenCover working with .NET Core, but it's Windows only.
Today, I'm exploring AltCover by Steve Gilham. There are coverage tools that use the .NET Profiling API at run-time, instead, AltCover weaves IL for its coverage.
As the name suggests, it's an alternative coverage approach. Rather than working by hooking the .net profiling API at run-time, it works by weaving the same sort of extra IL into the assemblies of interest ahead of execution. This means that it should work pretty much everywhere, whatever your platform, so long as the executing process has write access to the results file. You can even mix-and-match between platforms used to instrument and those under test.
AltCover is a NuGet package but it's also available as .NET Core Global Tool which is awesome.
dotnet tool install --global altcover.global
This makes "altcover" a command that's available everywhere without adding it to my project.
That said, I'm going to follow the AltCover Quick Start and see how quickly I can get it set up!
I'll Install into my test project hanselminutes.core.tests
dotnet add package AltCover
and then run
dotnet test /p:AltCover=true
Cool. My tests run as usual, but now I've got a coverage.xml in my test folder. I could also generate LCov or Cobertura reports if I'd like. At this point my coverage.xml is nearly a half-meg! That's a lot of good information, but how do I see the results in a human readable format?
This is the OpenCover XML format and I can run ReportGenerator on the coverage file and get a whole bunch of HTML files. Basically an entire coverage mini website!
I downloaded ReportGenerator and put it in its own folder (this would be ideal as a .NET Core global tool).
c:\ReportGenerator\ReportGenerator.exe -reports:coverage.xml -targetdir:./coverage
Make sure you use a decent targetDir otherwise you might end up with dozens of HTML files littered in your project folder. You might also consider .gitignoring the resulting folder and coverage file. Open up index.htm and check out all this great information!
Note the Risk Hotspots at the top there! I've got a CustomPageHandler with a significant NPath Complexity and two Views with a significant Cyclomatic Complexity.
Also check out the excellent branch coverage as expressed here in the results of the coverage report. You can see that EnableAutoLinks was always true, so I only ever tested one branch. I might want to add a negative test here and explore if there's any side effects with EnableAutoLinks is false.
Be sure to explore AltCover and its Full Usage Guide. There's a number of ways to run it, from global tools, dotnet test, MSBuild Tasks, and PowerShell integration!
- For use cases, see Use Cases.
- For modes of operation, see Modes of Operation.
- For driving AltCover from
dotnet test, seedotnet testintegration. - For driving AltCover from MSBuild, see MSBuild Tasks.
- For driving AltCover and associated tools with Windows PowerShell or PowerShell Core, see PowerShell integration.
There's a lot of great work here and it took me literally 10 minutes to get a great coverage report with AltCover and .NET Core. Kudos to Steve on AltCover! Head over to https://github.com/SteveGilham/altcover and give it a STAR, file issues (be kind) or perhaps offer to help out! And most of all, share cool Open Source projects like this with your friends and colleagues.
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About Scott
Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.
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Does that mean you should be creating separate artefacts in your
CI pipeline for coverage so as to avoid polluting your release dlls?
Loving this series of articles!
Take a look at minicover and let us know what you think.
Do you know any dotnet core compatible mutation framework that works on any dotnet core supported platform? I am used to pit test on Java platform (thanks to @unclebobmartin).
Kind regards,
Carlos Adriano Portes
I got stuck when the mutations generated invalid assemblies when replacing conditional jumps.
Maybe I did not understand all the differences associated with the .core version of Cecil.
There is a fork of NinjaTurtles on Github (NinjaTurtlesMutation) that I have not investigated.
I'm stuck trying to pull of a "dotnet tool install".
It is looking at my companies NuGet feed, where as the tool is I guess in the public feed?
So I get some error "unable to load the service index for source", but of course it isn't the correct source...
Any ideas?
I'm stuck and desperate for help.
Thanks in advance!
https://mva.microsoft.com/en-US/training-courses/aspnet-core-beginner-18153
i was very hesitant to look ito it given that i just picked up MVC, and some courses over complicate the Core setup, but the tutorial pace from beginner, intermediate, advance is easy to follow and understand, GOOD JOB and thanks.
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great article.
ReportGenerator is also available as a Global tool, a CLI tool packacke is also available.
They are currently available as "alpha" releases. "alpha" just means that they are not yet feature complete.
I also created a sample project which uses OpenCover, Coverlet and altcover to generate coverage reports: https://github.com/danielpalme/DotNetCoverageToolComparision.