Test Coverage Visualization

Introduced in GitLab 12.9.

With the help of GitLab CI/CD, you can collect the test coverage information of your favorite testing or coverage-analysis tool, and visualize this information inside the file diff view of your merge requests (MRs). This will allow you to see which lines are covered by tests, and which lines still require coverage, before the MR is merged.

How test coverage visualization works

Collecting the coverage information is done via GitLab CI/CD's artifacts reports feature. You can specify one or more coverage reports to collect, including wildcard paths. GitLab will then take the coverage information in all the files and combine it together.

For the coverage analysis to work, you have to provide a properly formatted Cobertura XML report to artifacts:reports:cobertura. This format was originally developed for Java, but most coverage analysis frameworks for other languages have plugins to add support for it, like:

• simplecov-cobertura (Ruby)
• gocover-cobertura (Golang)

Other coverage analysis frameworks support the format out of the box, for example:

• Istanbul (JavaScript)
• Coverage.py (Python)

Once configured, if you create a merge request that triggers a pipeline which collects coverage reports, the coverage will be shown in the diff view. This includes reports from any job in any stage in the pipeline. The coverage will be displayed for each line:

• covered (green): lines which have been checked at least once by tests
• no test coverage (orange): lines which are loaded but never executed
• no coverage information: lines which are non-instrumented or not loaded

Hovering over the coverage bar will provide further information, such as the number of times the line was checked by tests.

Example test coverage configuration

The following gitlab-ci.yml example uses Mocha JavaScript testing and NYC coverage-tooling to generate the coverage artifact:

test:
  script:
    - npm install
    - npx nyc --reporter cobertura mocha
  artifacts:
    reports:
      cobertura: coverage/cobertura-coverage.xml

Enabling the feature

This feature comes with the :coverage_report_view feature flag disabled by default. This feature is disabled due to some performance issues with very large data sets. When the performance issue is resolved, the feature will be enabled by default.

To enable this feature, ask a GitLab administrator with Rails console access to run the following command:

Feature.enable(:coverage_report_view)