Demo Unit Test and JaCoCo

In this hands-on guide, you'll learn how to configure a Jenkins Pipeline to run unit tests on a Spring Boot application and generate code coverage reports using the JaCoCo plugin. By visualizing test results and coverage metrics directly in Jenkins, you can maintain quality gates and improve code reliability.

Prerequisites

• A running Jenkins server (version 2.x or later)
• Jenkins plugins: Pipeline, JUnit, JaCoCo (v3.2.0+)
• A Spring Boot project with Maven build (pom.xml)
• Git repository with sample tests under src/test/java

1. Review the Unit Test Cases

Navigate to src/test/java and inspect the NumericApplicationTests class. It uses MockMvc to validate HTTP endpoints:

@RunWith(SpringRunner.class)
@SpringBootTest
@AutoConfigureMockMvc
public class NumericApplicationTests {
    @Autowired
    private MockMvc mockMvc;

    @Test
    public void smallerThanOrEqualToFiftyMessage() throws Exception {
        this.mockMvc.perform(get("/compare/49"))
            .andDo(print())
            .andExpect(status().isOk())
            .andExpect(content().string("Smaller than or equal to 50"));
    }

    @Test
    public void greaterThanFiftyMessage() throws Exception {
        this.mockMvc.perform(get("/compare/51"))
            .andDo(print())
            .andExpect(status().isOk())
            .andExpect(content().string("Greater than 50"));
    }

    @Test
    public void welcomeMessage() throws Exception {
        this.mockMvc.perform(get("/"))
            .andDo(print())
            .andExpect(status().isOk());
    }
}

2. Update Your Jenkinsfile to Run Unit Tests

Open the root Jenkinsfile. If you only build the artifact, insert a dedicated Unit Tests stage to execute mvn test:

pipeline {
    agent any

    stages {
        stage('Build - Maven') {
            steps {
                sh 'mvn clean package -DskipTests=true'
                archive 'target/*.jar'
            }
        }
        stage('Unit Tests') {
            steps {
                sh 'mvn test'
            }
        }
    }
}

Commit and push your changes to trigger a new build in Jenkins. Once the pipeline runs, you’ll see a stage summary:

The console logs will confirm all tests passed:

[INFO] Results:
[INFO] Tests run: 3, Failures: 0, Errors: 0, Skipped: 0
[INFO] BUILD SUCCESS

3. Configure JaCoCo in pom.xml

To collect coverage data, add the JaCoCo Maven plugin under the <build><plugins> section:

<plugin>
    <groupId>org.jacoco</groupId>
    <artifactId>jacoco-maven-plugin</artifactId>
    <version>0.8.5</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>

4. Publish JUnit and JaCoCo Reports in Jenkins

Ensure the Jenkins JaCoCo plugin (v3.2.0+) is installed under Manage Jenkins → Installed Plugins:

Then, refine the Unit Tests stage to archive JUnit results and publish coverage:

pipeline {
    agent any

    stages {
        stage('Build - Maven') {
            steps {
                sh 'mvn clean package -DskipTests=true'
                archive 'target/*.jar'
            }
        }
        stage('Unit Tests & Coverage') {
            steps {
                sh 'mvn test'
            }
            post {
                always {
                    // Publish JUnit results
                    junit 'target/surefire-reports/*.xml'
                    // Publish JaCoCo coverage
                    jacoco execPattern: 'target/jacoco.exec'
                }
            }
        }
    }
}

Commit and push again. After the build, Jenkins will display JaCoCo metrics in the console:

[jacoco plugin] Collecting JaCoCo coverage data...
[jacoco plugin] Overall coverage: class: 100.0, method: 71.43, line: 61.11, branch: 100.0, instruction: 40.91, complexity: 75.0

Navigate to the build’s Code Coverage Report for a breakdown by package and file:

Next Steps

With your unit tests and coverage reports in place, you can now build a Docker image for this Spring Boot application and push it to Docker Hub.

Links and References

• Jenkins Pipeline Documentation
• JaCoCo Maven Plugin
• Spring Boot Reference Guide
• JUnit 5 User Guide