Code coverage reports in Jenkins - Mini Project: Build & Apply

Code coverage reports

📖 Scenario: You are working on a software project that uses Jenkins for continuous integration. Your team wants to track how much of the code is tested by automated tests. This helps find untested parts and improve software quality.

🎯 Goal: Set up a Jenkins pipeline that runs tests and generates a code coverage report using a simple configuration. You will create the pipeline script step-by-step to collect and display coverage results.

📋 What You'll Learn

Create a Jenkins pipeline script with a pipeline block

Add a stage called Run Tests that runs a shell command to execute tests and generate coverage data

Add a stage called Publish Coverage that uses the publishCoverage step to publish the coverage report

Print a message confirming the coverage report was published

💡 Why This Matters

🌍 Real World

Code coverage reports help teams see how much of their code is tested automatically. This improves software quality and reduces bugs.

💼 Career

Many DevOps and CI/CD roles require setting up pipelines that run tests and publish coverage reports to ensure code quality.

1

Create the Jenkins pipeline skeleton

Create a Jenkins pipeline script starting with pipeline { and agent any inside it. Add an empty stages block inside the pipeline.

Jenkins

pipeline {
    agent any
    stages {
        // Your code here
    }
}

Hint

Start with pipeline {, then add agent any and an empty stages block.

2

Add a stage to run tests and generate coverage

Inside the stages block, add a stage named Run Tests. Inside it, add a steps block that runs the shell command sh 'make test coverage' to execute tests and generate coverage data.

Jenkins

pipeline {
    agent any
    stages {
        stage('Run Tests') {
            steps {
                // Your code here
            }
        }
    }
}

Hint

Use stage('Run Tests') with steps { sh 'make test coverage' } inside.

3

Add a stage to publish the coverage report

Add another stage inside stages named Publish Coverage. Inside it, add a steps block that calls publishCoverage adapters: [coberturaAdapter('coverage.xml')] to publish the coverage report from the file coverage.xml.

Jenkins

pipeline {
    agent any
    stages {
        stage('Run Tests') {
            steps {
                sh 'make test coverage'
            }
        }
        stage('Publish Coverage') {
            steps {
                // Your code here
            }
        }
    }
}

Hint

Use publishCoverage adapters: [coberturaAdapter('coverage.xml')] inside the Publish Coverage stage.

4

Print confirmation message after publishing coverage

Inside the Publish Coverage stage's steps block, after publishing coverage, add a echo step that prints 'Coverage report published successfully.'.

Jenkins

pipeline {
    agent any
    stages {
        stage('Run Tests') {
            steps {
                sh 'make test coverage'
            }
        }
        stage('Publish Coverage') {
            steps {
                publishCoverage adapters: [coberturaAdapter('coverage.xml')]
                // Your code here
            }
        }
    }
}

Hint

Add echo 'Coverage report published successfully.' after the publishCoverage step.

Practice

1. What is the main purpose of code coverage reports in Jenkins?

easy

A. To show which parts of the code are tested

B. To deploy the application automatically

C. To monitor server CPU usage

D. To manage user permissions

Solution

1. Step 1: Understand code coverage reports

   Code coverage reports indicate which parts of the source code have been executed during tests.

2. Step 2: Identify Jenkins role

   Jenkins uses these reports to help developers see test completeness and improve code quality.

3. Final Answer:

   To show which parts of the code are tested -> Option A

4. Quick Check:

   Code coverage = tested code parts [OK]

Hint: Coverage reports show tested code areas, not deployment [OK]

Common Mistakes:

• Confusing coverage with deployment
• Thinking coverage monitors server stats
• Mixing coverage with user management

2. Which Jenkins plugin is commonly used to publish Java code coverage reports?

easy

A. Git Plugin

B. JaCoCo Plugin

C. Docker Plugin

D. Slack Notification Plugin

Solution

1. Step 1: Identify coverage plugins for Java

   JaCoCo is a popular plugin for Java projects to generate code coverage reports in Jenkins.

2. Step 2: Exclude unrelated plugins

   Git manages source code, Docker manages containers, Slack sends messages, so they don't handle coverage.

3. Final Answer:

   JaCoCo Plugin -> Option B

4. Quick Check:

   Java coverage = JaCoCo [OK]

Hint: JaCoCo is the standard for Java coverage in Jenkins [OK]

Common Mistakes:

• Choosing Git for coverage
• Confusing Docker with coverage tools
• Selecting notification plugins

3. Given this Jenkins pipeline snippet, what will be the result of the jacoco step?

pipeline {
  agent any
  stages {
    stage('Test') {
      steps {
        junit '**/test-results.xml'
        jacoco execPattern: '**/jacoco.exec'
      }
    }
  }
}

medium

A. Publishes JaCoCo coverage report using the specified exec file

B. Runs unit tests and skips coverage report

C. Fails because jacoco is not a valid step

D. Publishes test results but ignores coverage data

Solution

1. Step 1: Understand the jacoco step usage

   The jacoco step in Jenkins pipeline publishes coverage reports using the exec file pattern provided.

2. Step 2: Analyze the snippet

   The pipeline runs tests with junit and then publishes coverage with jacoco execPattern: '**/jacoco.exec'.

3. Final Answer:

   Publishes JaCoCo coverage report using the specified exec file -> Option A

4. Quick Check:

   jacoco step publishes coverage report [OK]

Hint: jacoco step publishes coverage from exec files [OK]

Common Mistakes:

• Thinking jacoco runs tests
• Assuming jacoco step is invalid
• Ignoring coverage data in pipeline

4. You added the JaCoCo plugin to Jenkins but the coverage report does not appear after the build. What is the most likely cause?

medium

A. The Jenkins server is offline

B. The Jenkins user lacks admin rights

C. The build script does not run any tests

D. The jacoco.exec file path is incorrect or missing

Solution

1. Step 1: Check coverage report prerequisites

   JaCoCo needs the jacoco.exec file generated by tests to publish coverage.

2. Step 2: Identify common error

   If the exec file path is wrong or the file is missing, Jenkins cannot show the coverage report.

3. Final Answer:

   The jacoco.exec file path is incorrect or missing -> Option D

4. Quick Check:

   Missing exec file = no coverage report [OK]

Hint: Check jacoco.exec file path if coverage missing [OK]

Common Mistakes:

• Blaming Jenkins offline status
• Ignoring test execution for coverage
• Assuming user rights block coverage display

5. You want Jenkins to fail the build if code coverage falls below 80%. Which configuration should you add to the JaCoCo plugin in your pipeline?

hard

A. jacoco(execPattern: '**/jacoco.exec', failBuildIfCoverageLow: 80)

B. jacoco(execPattern: '**/jacoco.exec', changeBuildStatus: true, minimumCoverage: 80)

C. jacoco(execPattern: '**/jacoco.exec', changeBuildStatus: true, minimumInstructionCoverage: 80)

D. jacoco(execPattern: '**/jacoco.exec', coverageThreshold: 80)

Solution

1. Step 1: Understand JaCoCo coverage thresholds

   The JaCoCo plugin uses minimumInstructionCoverage to set the minimum coverage percentage for instructions.

2. Step 2: Identify correct syntax to fail build

   Setting changeBuildStatus: true with minimumInstructionCoverage: 80 makes Jenkins fail if coverage is below 80%.

3. Final Answer:

   jacoco(execPattern: '**/jacoco.exec', changeBuildStatus: true, minimumInstructionCoverage: 80) -> Option C

4. Quick Check:

   minimumInstructionCoverage + changeBuildStatus = fail below threshold [OK]

Hint: Use minimumInstructionCoverage with changeBuildStatus true [OK]

Common Mistakes:

• Using non-existent parameters like coverageThreshold
• Omitting changeBuildStatus to fail build
• Confusing minimumCoverage with minimumInstructionCoverage