I recently started using Coverlet for code coverage in some projects, the projects are all hosted on GitHub or Azure DevOps and build using MSBuild and Azure Pipelines. In this post I will describe how I'm using it.
What is Coverlet
Coverlet is a cross platform code coverage framework for .NET, with support for line, branch and method coverage. It works with .NET Framework on Windows and .NET Core on all supported platforms.
Coverlet also integrates with the build system to run code coverage after tests. Enabling code coverage is as simple as setting the
CollectCoverage property to
> dotnet test /p:CollectCoverage=true
Add Coverlet to the test projects
To add Coverlet to your test project use the following command.
> dotnet add package coverlet.msbuild
You can also add it to all of your test projects at once by adding a
Directory.Build.props file to your
Directory.Build.props files you can add a new property to every project in one step by defining it in the root folder that contains your source. When MSBuild runs,
Microsoft.Common.props searches your directory structure for the
Directory.Build.props file (and
Microsoft.Common.targets looks for
Directory.Build.targets). If it finds one, it imports the property.
<Project> <ItemGroup> <PackageReference Include="coverlet.msbuild" Version="2.6.3"> <PrivateAssets>all</PrivateAssets> <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets> </PackageReference> </ItemGroup> </Project>
Coverlet can generate coverage results in multiple formats, which is specified using the
CoverletOutputFormat property. For example, the following command emits coverage results in the
> dotnet test /p:CollectCoverage=true /p:CoverletOutputFormat=cobertura
Include and/or exclude code
You can ignore a method or an entire class from code coverage by creating and applying the
ExcludeFromCodeCoverage attribute present in the
Coverlet also gives you the ability to have fine grained control over what gets excluded or included using "filter expressions". In the following example we include all projects that start with
CompanyName., and exclude all projects that end with
> dotnet test /p:CollectCoverage=true /p:Include="[CompanyName.*]*" /p:Exclude="[*Tests]*"
Note: To exclude or include multiple assemblies when using Powershell scripts or creating a .yaml file for a Azure DevOps build
%2cshould be used as a separator. MSBuild will translate this symbol to
In a Azure Pipeline you can use the .NET Core CLI task to run your tests. You have to add some extra arguments to enable the coverage.
Configure the test to collect coverage
To run the code coverage in our Azure Pipeline we need to configure the .NET Core CLI task. We can use the arguments from the
dotnet test command.
- task: DotNetCoreCLI@2 displayName: Test inputs: command: test projects: | **/tests/*.Tests/*.csproj arguments: '--configuration $(buildConfiguration) /p:CollectCoverage=true /p:CoverletOutputFormat=cobertura /p:Include="[ProjectName.*]*" /p:Exclude="[*Tests]*"'
Generate the code coverage report
To generate the code coverage report from the individual code coverage results per test project, you can use the ReportGenerator task. ReportGenerator converts coverage reports generated by a number of reporters into human readable reports in various formats.
- task: Palmmedia.reportgenerator.reportgenerator-build-release-task.reportgenerator@4 displayName: Generate Code Coverage Report inputs: reports: $(Build.SourcesDirectory)/tests/**/coverage.cobertura.xml targetdir: $(build.artifactstagingdirectory)/TestResults/ reporttypes: 'HtmlInline_AzurePipelines;Cobertura;Badges'
Publish the code coverage results
Publish the code coverage results with the Publish Code Coverage Results task
- task: PublishCodeCoverageResults@1 displayName: 'Publish Code Coverage Results' inputs: codeCoverageTool: cobertura summaryFileLocation: $(build.artifactstagingdirectory)/TestResults/cobertura.xml # To make the task not regenerate the report an environment variable was added to the pipeline in Azure DevOps; "disable.coverage.autogenerate: 'true'" # see: https://github.com/danielpalme/ReportGenerator/wiki/Integration#attention reportDirectory: '$(build.artifactstagingdirectory)/TestResults'
The Publish Code Coverage Results task from Microsoft regenerates the report with different settings and based on the supplied Coberatura file. Moreover it does not necessarily use the latest version of ReportGenerator. To disable the regeneration of the report, you need to use the following environment variable in your build (in Azure DevOps).