Code coverage reports in Jenkins - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Jenkins Pipeline: Code Coverage Report Generation

Given this Jenkins pipeline snippet, what will be the output after running the jacoco step?

Jenkins

pipeline {
  agent any
  stages {
    stage('Build') {
      steps {
        echo 'Building project...'
      }
    }
    stage('Test') {
      steps {
        echo 'Running tests...'
      }
    }
    stage('Code Coverage') {
      steps {
        jacoco execPattern: '**/target/*.exec', classPattern: '**/classes', sourcePattern: '**/src/main/java'
      }
    }
  }
}

A The pipeline runs but does not generate any coverage report because no test execution is specified.

B The pipeline generates a JaCoCo code coverage report and archives it in Jenkins for visualization.

C The pipeline fails because the <code>jacoco</code> step is not recognized in Jenkins pipelines.

D The pipeline generates a test report but no code coverage report.

💡 Hint

The jacoco step in Jenkins pipelines is used to collect and publish code coverage reports.

The jacoco step collects coverage data from the specified exec files and generates a report Jenkins can display. It requires the JaCoCo plugin installed.

❓ Troubleshoot

intermediate

Troubleshooting Missing Coverage Data in Jenkins

A Jenkins job runs tests and uses JaCoCo for coverage, but the coverage report shows 0% coverage. What is the most likely cause?

A The JaCoCo exec files were not generated because tests did not run with the JaCoCo agent enabled.

B The Jenkins workspace was cleaned before running tests, deleting coverage data.

C The <code>jacoco</code> step was placed before the test execution stage in the pipeline.

D The Jenkins server does not have enough memory to generate the coverage report.

💡 Hint

Coverage data depends on tests running with the coverage agent active.

If tests run without the JaCoCo agent, no coverage data is collected, resulting in 0% coverage report.

❓ Configuration

advanced

Configuring Jenkins to Fail Build on Low Coverage

Which Jenkins pipeline snippet correctly fails the build if code coverage is below 80% using JaCoCo plugin?

A jacoco execPattern: '**/target/*.exec', classPattern: '**/classes', sourcePattern: '**/src/main/java', changeBuildStatus: true, minimumInstructionCoverage: '80'

B jacoco execPattern: '**/target/*.exec', classPattern: '**/classes', sourcePattern: '**/src/main/java', minimumInstructionCoverage: 80, failBuild: true

C jacoco execPattern: '**/target/*.exec', classPattern: '**/classes', sourcePattern: '**/src/main/java', changeBuildStatus: true, minimumInstructionCoverage: '80%'

D jacoco execPattern: '**/target/*.exec', classPattern: '**/classes', sourcePattern: '**/src/main/java', failBuildOnLowCoverage: true, minimumCoverage: 80

💡 Hint

Check the official JaCoCo plugin documentation for correct parameter names and types.

The changeBuildStatus parameter set to true enables build failure on coverage below thresholds. The threshold values are strings without % sign.

🔀 Workflow

advanced

Best Workflow to Collect Coverage from Multiple Modules

You have a multi-module Maven project. How should you configure Jenkins to collect JaCoCo coverage reports from all modules correctly?

A Run tests only in the root module and use <code>jacoco</code> step with execPattern '**/target/*.exec' to collect coverage.

B Run tests separately for each module and call <code>jacoco</code> step individually for each module's exec file.

C Run <code>mvn clean install</code> and rely on Jenkins to auto-detect coverage files without specifying patterns.

D Run <code>mvn clean verify</code> at root, then use <code>jacoco</code> step with execPattern '**/target/*.exec' to collect all coverage files.

💡 Hint

Maven multi-module builds generate coverage files in each module's target directory.

Running mvn clean verify at root runs tests in all modules. Using a wildcard execPattern collects all coverage files for combined report.

✅ Best Practice

expert

Ensuring Accurate Coverage Reports in Jenkins Pipelines

Which practice ensures the most accurate and reliable code coverage reports in Jenkins pipelines using JaCoCo?

A Run tests without JaCoCo agent and rely on Jenkins to generate coverage from compiled classes.

B Run <code>jacoco</code> step before tests to initialize coverage collection, then run tests normally.

C Run tests with JaCoCo agent enabled, archive exec files as artifacts, and run <code>jacoco</code> step after tests complete.

D Run tests with JaCoCo agent but do not archive exec files; just run <code>jacoco</code> step to generate report.

💡 Hint

Coverage data must be collected during test execution and preserved for reporting.

Enabling JaCoCo agent during tests collects coverage data. Archiving exec files ensures data is available for report generation after tests.

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