Target audience

.NET Core developers using Travis CI builds who want code coverage automatically generated and uploaded to Coveralls.

Generating code coverage

Add the coverlet.msbuild NuGet package to your test project:

dotnet add package coverlet.msbuild

This adds code coverage support to dotnet test by passing the /p:CollectCoverage=true parameter. Providing this parameter will cause the test run to output code coverage results on the console as well as write them to a file coverage.json.

Coveralls

Coveralls is a free service for uploading code coverage for history tracking and statistics. Sign up, link your GitHub repository, and you'll get a token (which you should keep private!) for uploading code coverage files.

Coveralls only supports particular code coverage formats, but one of those is OpenCover, which Coverlet supports with /p:CoverletOutputFormat=opencover.

Travis CI

Travis CI is a free continuous integration platform for building and testing open source projects. It builds your project by spinning up fresh Ubuntu VM, configuring it according to the .travis.yml file at the root of your repository, and running commands within it. Link your repository and set up that file and you should get a working build. A basic .NET Core .travis.yml file can look like this:

language: csharp
mono: none
dotnet: 2.1.300

install:
- dotnet restore

script:
 - dotnet build
 - dotnet test

Travis CI also supports managing environment variables so they don't have to be checked into scripts/publicly available in your project. This is great for the Coveralls token you got earlier. Set that up in Travis by going to More Options -> Settings and scrolling down to Environment Variables. Name your variable COVERALLS_REPO_TOKEN and paste the value in, leaving "Display value in build log" unchecked.

Putting it all together

We're going to add code coverage generation to our Travis CI build and then use a dotnet tool called coveralls.net to upload it to Coveralls all automatically at the end of the build.

The updated .travis.yml

language: csharp
mono: none
dotnet: 2.1.300

install:
- dotnet restore

script:
 - dotnet build
 - dotnet test
 - dotnet tool install --global coveralls.net --version 1.0.0
 - export PATH="$PATH:/home/travis/.dotnet/tools"
 - csmacnz.Coveralls --opencover -i /path/to/coverage.opencover.xml --useRelativePaths --commitId $TRAVIS_COMMIT --commitBranch $TRAVIS_BRANCH --commitAuthor "$REPO_COMMIT_AUTHOR" --commitEmail "$REPO_COMMIT_AUTHOR_EMAIL" --commitMessage "$REPO_COMMIT_MESSAGE" --jobId $TRAVIS_JOB_ID  --serviceName travis-ci

If everything works right your Travis CI build should succeed and you should see code coverage results on Coveralls and your commit history on GitHub!

References

• http://tattoocoder.com/cross-platform-code-coverage-arrives-for-net-core/
• https://medium.com/@tonerdo/setting-up-coveralls-with-coverlet-for-a-net-core-project-2c8ec6c5dc58
• https://docs.coveralls.io/
• https://github.com/csmacnz/coveralls.net\
• https://docs.travis-ci.com/user/coveralls/
• https://docs.travis-ci.com/user/environment-variables/