Code coverage reports in Jenkins - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a code coverage report in Jenkins?

A code coverage report shows how much of your source code is tested by automated tests. It helps find untested parts to improve quality.

beginner

Which Jenkins plugin is commonly used to generate code coverage reports?

The 'JaCoCo' plugin is commonly used in Jenkins to collect and display Java code coverage reports.

intermediate

How do you publish a JaCoCo code coverage report in a Jenkins pipeline?

Use the 'jacoco' step in your Jenkinsfile after tests run, for example:

jacoco execPattern: '**/jacoco.exec'

This publishes the coverage report in Jenkins UI.

beginner

What does a high code coverage percentage mean?

It means most of your code is tested by automated tests, which usually leads to fewer bugs and better software quality.

intermediate

Can code coverage reports guarantee bug-free software?

No, code coverage shows tested code parts but does not guarantee no bugs. Tests must be well written and cover important cases.

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

A To show how much code is tested by automated tests

B To deploy code to production

C To monitor server health

D To manage user permissions

Code coverage reports help identify which parts of the code are tested, improving test completeness.

Which plugin is typically used in Jenkins for Java code coverage?

A Git plugin

B JaCoCo plugin

C Docker plugin

D Slack plugin

JaCoCo plugin collects and displays Java code coverage reports in Jenkins.

In a Jenkins pipeline, where should the code coverage step be placed?

A Before checkout

B Before running tests

C After running tests

D After deployment

Code coverage is collected after tests run to analyze which code was executed.

What does a low code coverage percentage indicate?

A Few parts of code are tested

B Most code is tested

C Tests are perfect

D Code is bug-free

Low coverage means many code parts lack automated tests.

Does 100% code coverage guarantee no bugs?

A Yes, always

B Only for small projects

C Only if tests run fast

D No, tests might miss cases

Even full coverage can't guarantee no bugs if tests don't check all scenarios.

Explain what a code coverage report is and why it is useful in Jenkins pipelines.

Think about how tests relate to code parts.

Describe how to set up and publish a JaCoCo code coverage report in a Jenkins pipeline.

Focus on the pipeline steps and plugin usage.

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