• How test coverage visualization works
  • Artifact expiration
  • Automatic class path correction
    • Path correction example
• Example test coverage configurations
  • JavaScript example
  • Java and Kotlin examples
    • Maven example
    • Gradle example
  • Python example
  • C/C++ example

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.

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 then takes the coverage information in all the files and combines 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 is shown in the diff view. This includes reports from any job in any stage in the pipeline. The coverage displays 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 provides further information, such as the number of times the line was checked by tests.

Artifact expiration

By default, the pipeline artifact used to draw the visualization on the merge request expires one week after creation.

Automatic class path correction

The coverage report properly matches changed files only if the filename of a class element contains the full path relative to the project root. However, in some coverage analysis frameworks, the generated Cobertura XML has the filename path relative to the class package directory instead.

To make an intelligent guess on the project root relative class path, the Cobertura XML parser attempts to build the full path by:

• Extracting a portion of the source paths from the sources element and combining them with the class filename path.
• Checking if the candidate path exists in the project.
• Using the first candidate that matches as the class full path.

Path correction example

As an example, a project with:

• A full path of test-org/test-project.

• The following files relative to the project root:

  Auth/User.cs
  Lib/Utils/User.cs
  src/main/java
  

In the:

• Cobertura XML, the filename attribute in the class element assumes the value is a relative path to the project’s root:

  <class name="packet.name" filename="src/main/java" line-rate="0.0" branch-rate="0.0" complexity="5">
  

• sources from Cobertura XML, the following paths in the format <CI_BUILDS_DIR>/<PROJECT_FULL_PATH>/...:

  <sources>
    <source>/builds/test-org/test-project/Auth</source>
    <source>/builds/test-org/test-project/Lib/Utils</source>
  </sources>
  

The parser:

• Extracts Auth and Lib/Utils from the sources and uses these to determine the class path relative to the project root.
• Combines these extracted sources and the class filename. For example, if there is a class element with the filename value of User.cs, the parser takes the first candidate path that matches, which is Auth/User.cs.
• For each class element, attempts to look for a match for each extracted source path up to 100 iterations. If it reaches this limit without finding a matching path in the file tree, the class is not included in the final coverage report.

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 choose an existing stage like `deploy`.
  stage: visualize
  image: registry.gitlab.com/haynes/jacoco2cobertura:1.0.7
  script:
    # convert report from jacoco to cobertura, using relative project path
    - python /opt/cover2cover.py target/site/jacoco/jacoco.xml $CI_PROJECT_DIR/src/main/java/ > 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: registry.gitlab.com/haynes/jacoco2cobertura:1.0.7
  script:
    # convert report from jacoco to cobertura, using relative project path
    - python /opt/cover2cover.py build/jacoco/jacoco.xml $CI_PROJECT_DIR/src/main/java/ > 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

C/C++ example

The following gitlab-ci.yml example for C/C++ with gcc or g++ as the compiler uses gcovr to generate the coverage output file in Cobertura XML format.

This example assumes:

• That the Makefile is created by cmake in the build directory, within another job in a previous stage. (If you use automake to generate the Makefile, then you need to call make check instead of make test.)
• cmake (or automake) has set the compiler option --coverage.

run tests:
  stage: test
  script:
    - cd build
    - make test
    - gcovr --xml-pretty --exclude-unreachable-branches --print-summary -o coverage.xml --root ${CI_PROJECT_DIR}
  coverage: /^\s*lines:\s*\d+.\d+\%/
  artifacts:
    name: ${CI_JOB_NAME}-${CI_COMMIT_REF_NAME}-${CI_COMMIT_SHA}
    expire_in: 2 days
    reports:
      cobertura: build/coverage.xml