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Test Coverage Visualization

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.

Test Coverage Visualization Diff View

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:

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

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.

NOTE: The Cobertura XML parser currently does not support the sources element and ignores it. It is assumed that the filename of a class element contains the full path relative to the project root.

Example test coverage configurations

JavaScript example

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

Java and Kotlin examples

Maven example

The following gitlab-ci.yml example for Java or Kotlin uses Maven to build the project and JaCoCo coverage-tooling to generate the coverage artifact. You can check the Docker image configuration and scripts if you want to build your own image.

GitLab expects the artifact in the Cobertura format, so you have to execute a few scripts before uploading it. The test-jdk11 job tests the code and generates an XML artifact. The coverage-jdk-11 job converts the artifact into a Cobertura report:

test-jdk11:
  stage: test
  image: maven:3.6.3-jdk-11
  script:
    - 'mvn $MAVEN_CLI_OPTS clean org.jacoco:jacoco-maven-plugin:prepare-agent test jacoco:report'
  artifacts:
    paths:
      - target/site/jacoco/jacoco.xml

coverage-jdk11:
  # Must be in a stage later than test-jdk11's stage.
  # The `visualize` stage does not exist by default.
  # Please define it first, or chose an existing stage like `deploy`.
  stage: visualize
  image: haynes/jacoco2cobertura:1.0.4
  script:
    # convert report from jacoco to cobertura
    - 'python /opt/cover2cover.py target/site/jacoco/jacoco.xml src/main/java > target/site/cobertura.xml'
    # read the <source></source> tag and prepend the path to every filename attribute
    - 'python /opt/source2filename.py target/site/cobertura.xml'
  needs: ["test-jdk11"]
  dependencies:
    - test-jdk11
  artifacts:
    reports:
      cobertura: target/site/cobertura.xml

Gradle example

The following gitlab-ci.yml example for Java or Kotlin uses Gradle to build the project and JaCoCo coverage-tooling to generate the coverage artifact. You can check the Docker image configuration and scripts if you want to build your own image.

GitLab expects the artifact in the Cobertura format, so you have to execute a few scripts before uploading it. The test-jdk11 job tests the code and generates an XML artifact. The coverage-jdk-11 job converts the artifact into a Cobertura report:

test-jdk11:
  stage: test
  image: gradle:6.6.1-jdk11
  script:
    - 'gradle test jacocoTestReport' # jacoco must be configured to create an xml report
  artifacts:
    paths:
      - build/jacoco/jacoco.xml

coverage-jdk11:
  # Must be in a stage later than test-jdk11's stage.
  # The `visualize` stage does not exist by default.
  # Please define it first, or chose an existing stage like `deploy`.
  stage: visualize
  image: haynes/jacoco2cobertura:1.0.4
  script:
    # convert report from jacoco to cobertura
    - 'python /opt/cover2cover.py build/jacoco/jacoco.xml src/main/java > build/cobertura.xml'
    # read the <source></source> tag and prepend the path to every filename attribute
    - 'python /opt/source2filename.py build/cobertura.xml'
  needs: ["test-jdk11"]
  dependencies:
    - test-jdk11
  artifacts:
    reports:
      cobertura: build/cobertura.xml

Python example

The following gitlab-ci.yml example for Python uses pytest-cov to collect test coverage data and coverage.py to convert the report to use full relative paths. The information isn't displayed without the conversion.

This example assumes that the code for your package is in src/ and your tests are in tests.py:

run tests:
  stage: test
  image: python:3
  script:
    - pip install pytest pytest-cov
    - pytest --cov=src/ tests.py
    - coverage xml
  artifacts:
    reports:
      cobertura: coverage.xml