Test coverage visualization

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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 allows 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 by using the GitLab CI/CD 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. Coverage files are parsed in a background job so there can be a delay between pipeline completion and the visualization loading on the page.

For the coverage analysis to work, you have to provide a properly formatted Cobertura XML report to artifacts:reports:coverage_report. 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 (Go)

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

Istanbul (JavaScript)
Coverage.py (Python)
PHPUnit (PHP)

After configuration, if your merge request triggers a pipeline that collects coverage reports, the coverage information is displayed 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.

Uploading a test coverage report does not enable:

You must configure these separately.

Limits

A limit of 100 <source> nodes for Cobertura format XML files applies. If your Cobertura report exceeds 100 nodes, there can be mismatches or no matches in the merge request diff view.

A single Cobertura XML file can be no more than 10 MiB. For large projects, split the Cobertura XML into smaller files. See this issue for more details. When submitting many files, it can take a few minutes for coverage to show on a merge request.

The visualization only displays after the pipeline is complete. If the pipeline has a blocking manual job, the pipeline waits for the manual job before continuing and is not considered complete. The visualization cannot be displayed if the blocking manual job did not run.

Data expiration

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

Coverage report from child pipeline

Introduced in GitLab 15.1 with a flag named ci_child_pipeline_coverage_reports. Disabled by default.

Enabled on GitLab.com and self-managed and feature flag ci_child_pipeline_coverage_reports removed in GitLab 15.2.

If a job in a child pipeline creates a coverage report, the report is included in the parent pipeline's coverage report.

child_test_pipeline:
  trigger:
    include:
      - local: path/to/child_pipeline_with_coverage.yml

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 C# project with:

A full path of test-org/test-cs-project.
The following files relative to the project root:
```
Auth/User.cs
Lib/Utils/User.cs
```

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

<sources>
  <source>/builds/test-org/test-cs-project/Auth</source>
  <source>/builds/test-org/test-cs-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.

Automatic class path correction also works for a Java project with:

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

The following files relative to the project root:

src/main/java/com/gitlab/security_products/tests/App.java

sources from Cobertura XML:

<sources>
  <source>/builds/test-org/test-java-project/src/main/java/</source>
</sources>

class element with the filename value of com/gitlab/security_products/tests/App.java:

<class name="com.gitlab.security_products.tests.App" filename="com/gitlab/security_products/tests/App.java" line-rate="0.0" branch-rate="0.0" complexity="6.0">

NOTE: Automatic class path correction only works on source paths in the format <CI_BUILDS_DIR>/<PROJECT_FULL_PATH>/.... The source is ignored if the path does not follow this pattern. The parser assumes that the filename of a class element contains the full path relative to the project root.

Example test coverage configurations

This section provides test coverage configuration examples for different programming languages. You can also see a working example in the coverage-report demonstration project.

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:
      coverage_report:
        coverage_format: cobertura
        path: 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:1.0.9
  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"]
  artifacts:
    reports:
      coverage_report:
        coverage_format: cobertura
        path: 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.

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"]
  artifacts:
    reports:
      coverage_report:
        coverage_format: cobertura
        path: build/cobertura.xml

Python example

The following .gitlab-ci.yml example uses pytest-cov to collect test coverage data:

run tests:
  stage: test
  image: python:3
  script:
    - pip install pytest pytest-cov
    - pytest --cov --cov-report term --cov-report xml:coverage.xml
  artifacts:
    reports:
      coverage_report:
        coverage_format: cobertura
        path: coverage.xml

PHP example

The following .gitlab-ci.yml example for PHP uses PHPUnit to collect test coverage data and generate the report.

With a minimal phpunit.xml file (you may reference this example repository), you can run the test and generate the coverage.xml:

run tests:
  stage: test
  image: php:latest
  variables:
    XDEBUG_MODE: coverage
  before_script:
    - apt-get update && apt-get -yq install git unzip zip libzip-dev zlib1g-dev
    - docker-php-ext-install zip
    - pecl install xdebug && docker-php-ext-enable xdebug
    - php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
    - php composer-setup.php --install-dir=/usr/local/bin --filename=composer
    - composer install
    - composer require --dev phpunit/phpunit phpunit/php-code-coverage
  script:
    - php ./vendor/bin/phpunit --coverage-text --coverage-cobertura=coverage.cobertura.xml
  artifacts:
    reports:
      coverage_report:
        coverage_format: cobertura
        path: coverage.cobertura.xml

Codeception, through PHPUnit, also supports generating Cobertura report with run. The path for the generated file depends on the --coverage-cobertura option and paths configuration for the unit test suite. Configure .gitlab-ci.yml to find Cobertura in the appropriate path.

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}
  artifacts:
    name: ${CI_JOB_NAME}-${CI_COMMIT_REF_NAME}-${CI_COMMIT_SHA}
    expire_in: 2 days
    reports:
      coverage_report:
        coverage_format: cobertura
        path: build/coverage.xml

Go example

The following .gitlab-ci.yml example for Go uses:

go test to run tests.
gocover-cobertura to convert Go's coverage profile into the Cobertura XML format.

This example assumes that Go modules are being used. The -covermode count option does not work with the -race flag. If you want to generate code coverage while also using the -race flag, you must switch to -covermode atomic which is slower than -covermode count. See this blog post for more details.

run tests:
  stage: test
  image: golang:1.17
  script:
    - go install
    - go test ./... -coverprofile=coverage.txt -covermode count
    - go get github.com/boumenot/gocover-cobertura
    - go run github.com/boumenot/gocover-cobertura < coverage.txt > coverage.xml
  artifacts:
    reports:
      coverage_report:
        coverage_format: cobertura
        path: coverage.xml

Ruby example

The following .gitlab-ci.yml example for Ruby uses

rspec to run tests.
simplecov and simplecov-cobertura to record the coverage profile and create a report in the Cobertura XML format.

This example assumes:

That bundler is being used for dependency management. The rspec, simplecov and simplecov-cobertura gems have been added to your Gemfile.
The CoberturaFormatter has been added to your SimpleCov.formatters configuration within the spec_helper.rb file.

run tests:
  stage: test
  image: ruby:3.1
  script:
    - bundle install
    - bundle exec rspec
  artifacts:
    reports:
      coverage_report:
        coverage_format: cobertura
        path: coverage/coverage.xml

Troubleshooting

Test coverage visualization not displayed

If the test coverage visualization is not displayed in the diff view, you can check the coverage report itself and verify that:

The file you are viewing in the diff view is mentioned in the coverage report.
The source and filename nodes in the report follows the expected structure to match the files in your repository.
The pipeline has completed. If the pipeline is blocked on a manual job, the pipeline is not considered complete.
The coverage report file does not exceed the limits.

Report artifacts are not downloadable by default. If you want the report to be downloadable from the job details page, add your coverage report to the artifact paths:

artifacts:
  paths:
    - coverage/cobertura-coverage.xml
  reports:
    coverage_report:
      coverage_format: cobertura
      path: coverage/cobertura-coverage.xml