Creating Unit Test Coverage Reports for ASP.NET Core 3.1 Projects with Coverlet and ReportGenerator

Unit testing is an essential part of software development to ensure code quality and refactorability. In Agile projects, code can change rapidly, and thus it is often necessary to keep the unit tests and its coverage in check. It would be a good idea for reports to be generated to easily monitor the status of unit tests.

The HomeBrew Project

We are going to work with a simple project to demonstrate unit test reporting.

We have an ASP.NET Core 3.1 Web API Project called HomeBrew. For simplicity, it has a single BeerController which only contains API endpoints for retrieving currently available (in-memory-stored) beer varieties. These endpoints also have some tests already set up in HomeBrew.Tests > Controllers > BeerController - making sure that all beer varieties are actually retrieved and single beer retrieval actually works.

Our goal is to be able to generate HTML reports for the HomeBrew project’s available unit tests.

Installing the Requirements

First we need Coverlet - a code coverage framework. Add it to the HomeBrew.Tests project by running:

dotnet add package coverlet.collector

For Coverlet to work, 16.5.0 and above of Microsoft.NET.Test.Sdk should be referenced. So if it’s not there yet, add the following to HomeBrew.Tests.csproj:

<PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.5.0" />

Next, we need ReportGenerator to convert the Coverlet reports in human-friendly format - HTML to be exact. Add it to the HomeBrew.Tests project by running:

dotnet add package ReportGenerator

To be enable us to generate the reports via commandline, install the ReportGenerator global tool by running:

dotnet tool install --global dotnet-reportgenerator-globaltool --version 4.8.1

Generating the Reports

Run Coverlet using the following command in the HomeBrew.Tests project:

dotnet test --collect:"XPlat Code Coverage"

This will run the unit tests and automatically generate a Cobertura-format XML file containing the coverage results in a TestResults directory.

The XML file is then fed into ReportGenerator:

reportgenerator -reports:./TestResults/\*/\*.xml -targetdir:./Reports

This converts the Cobertura XML file into an HTML report of the unit test coverage in the specified directory Reports. Opening the index.html would show the coverage of our unit tests and allow line-per-line code exploration for us to see that the BeerController endpoints are fully covered.

Conclusion

Unit test reporting should be quick and simple with Coverlet and ReportGenerator. Automated reports can be done via CLI using these two tools and can be integrated into a CI/CD pipeline - perhaps for every code pull request or before every server deployment. This will help ensure that code quality is tracked and monitored in important phases of the software development cycle.