the question is what part of Coverage you want to see/have:

• just a number within the MR - therefore GitLab parses the logoutput of the Jobs
• coverage visualization within MR - therefore you need to provide a report.

Coverage in Overview

For the coverage in the Overview and just to get a percentage, you need to configure your job with an regex how it can be parsed like

job1:
  # ....
  coverage: '/Code coverage: \d+\.\d+/'

https://docs.gitlab.com/ee/ci/yaml/#coverage

Visualization

We are actually using JaCoCo, but to make the coverage visible and to have the information in Merge Requests you have to convert everything into Cobertura Reports.

There are different approaches to achieve this:

1. with a gradle-plugin like https://github.com/kageiit/gradle-jacobo-plugin

   the configuration is pretty neat, and if you do have already a gradle build it is easy to integrate

2. with an own step within the CI Pipeline - see https://docs.gitlab.com/ee/user/project/merge_requests/test_coverage_visualization.html

   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:
          cobertura: build/cobertura.xml
   

important to note is that you always will have to tell GitLab CI your path to the artifact for cobertura with

job:
    #...
    artifacts:
      reports:
        cobertura: build/cobertura.xml