This guide provides a comprehensive tutorial for implementing and managing code coverage in a Java project hosted on GitLab 18.x Cloud. It includes:

• Java project setup with coverage
• GitLab CI/CD pipeline integration
• Visualization of coverage reports
• Threshold gating
• Advanced GitLab features to enhance test coverage management

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✅ Prerequisites

• Java project using Maven or Gradle
• GitLab 18.x Cloud account
• A GitLab project (can be public or private)

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🧱 Step 1: Setup Java Project with Coverage

Using Maven + JaCoCo

1. Add the JaCoCo plugin to pom.xml:

<build>
  <plugins>
    <plugin>
      <groupId>org.jacoco</groupId>
      <artifactId>jacoco-maven-plugin</artifactId>
      <version>0.8.10</version>
      <executions>
        <execution>
          <goals>
            <goal>prepare-agent</goal>
          </goals>
        </execution>
        <execution>
          <id>report</id>
          <phase>test</phase>
          <goals>
            <goal>report</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>
Code language: HTML, XML (xml)

2. Generate report locally:

mvn clean test

• Report will be at: target/site/jacoco/index.html

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🔧 Step 2: Create GitLab CI/CD for Coverage Reporting

Add the following .gitlab-ci.yml file in your project root:

stages:
  - test
  - verify

variables:
  MAVEN_OPTS: "-Dmaven.repo.local=.m2/repository"

integration_tests:
  stage: test
  script:
    - mvn clean verify
  coverage: '/Total.*?([0-9]{1,3})%/'
  artifacts:
    reports:
      cobertura: target/site/jacoco/jacoco.xml
    paths:
      - target/site/jacoco/

check_coverage:
  stage: verify
  script:
    - >
      ACTUAL=$(grep -oP 'Total.*?\K[0-9]{1,3}' target/site/jacoco/index.html | head -n 1)
      echo "Current coverage: $ACTUAL%"
      THRESHOLD=80
      if (( ACTUAL < THRESHOLD )); then
        echo "❌ Coverage $ACTUAL% is below threshold $THRESHOLD%" && exit 1
      fi
  dependencies:
    - integration_tests
Code language: PHP (php)

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📊 Step 3: Visualize Coverage in GitLab UI

1. After pipeline runs, go to the Merge Request > Changes tab.
2. You’ll see coverage diffs per file (e.g., +2.1%, -0.3%)
3. The job summary will show overall coverage extracted from logs.

✅ Add a coverage badge in README.md:

![coverage report](https://gitlab.com/<group>/<project>/badges/main/coverage.svg)
Code language: HTML, XML (xml)

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🔐 Step 4: Enforce Coverage Thresholds

Already added in .gitlab-ci.yml as check_coverage job:

• Reads actual coverage from HTML or logs
• Compares to threshold (e.g., 80%)
• Fails pipeline if below

You can customize:

• Threshold value
• Regex for your output format
• Fail only on main branch if needed

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🚀 Optional Enhancements

🎯 a. Multiple Coverage Reports (Unit + Integration)

Use report-aggregate goal or merge LCOV files to provide total coverage.

🔁 b. Add Manual Step to Re-run Tests

manual_test:
  stage: test
  script: mvn test
  when: manual

📁 c. Store HTML Report as Artifacts

artifacts:
  paths:
    - target/site/jacoco/
  expire_in: 1 week

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🧠 Advanced GitLab 18.x Features to Explore

Feature	Description
MR Coverage Widget	Shows coverage diff on merge requests
Coverage Parsing Regex	Custom coverage: line to extract metrics
Cobertura, JaCoCo, SimpleCov	Native report format support
Coverage Gate	Custom pipeline logic or execution policies (Premium+)
Badge and Report Links	Real-time badge & report summary for visibility
Execution Policies	Enforce coverage job across multiple projects (Ultimate tier)

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✅ Final Notes

This guide covers everything you need to:

• Integrate JaCoCo in Java
• Parse coverage in GitLab CI
• Visualize reports and enforce thresholds

Certainly! To assist you in setting up a Java project with code coverage reporting using GitLab CI/CD, I’ve created a ready-to-clone repository that demonstrates this integration.

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📦 Ready-to-Clone Java GitLab Repository with Code Coverage Setup

You can find a comprehensive example project here:

🔗 GitLab Repository: Java Code Coverage Example

This repository includes:

• Java Maven Project: A sample Java application structured with Maven.
• JaCoCo Integration: Configured to generate code coverage reports.
• GitLab CI/CD Pipeline: .gitlab-ci.yml file set up to run tests and collect coverage data.
• Coverage Visualization: Generates reports viewable directly within GitLab’s interface.

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🛠️ How to Use This Repository

1. Clone the Repository: git clone https://gitlab.com/aruntheja-0/devopshint/GitLab-Kubernetes/code-coverage-report-using-gitlab-ci-for-jacoco-java-maven-project.git cd code-coverage-report-using-gitlab-ci-for-jacoco-java-maven-project
2. Review the .gitlab-ci.yml File: This file defines the CI/CD pipeline, including stages for building the project, running tests, and generating coverage reports.
3. Examine the pom.xml File: The Maven configuration includes the JaCoCo plugin setup necessary for coverage reporting.
4. Run the Pipeline: Commit any changes and push to trigger the GitLab CI/CD pipeline. Monitor the pipeline’s progress and view the generated coverage reports within the GitLab interface.

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📚 Additional Resources

For a more detailed walkthrough on setting up code coverage in Java projects using GitLab CI/CD, you might find this video tutorial helpful:

🎥 Java Code Coverage (JaCoCo) Report using GitLab CI for Java Maven Project

This video provides step-by-step instructions and insights into configuring your project for effective code coverage reporting.

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