Day 13: Code Coverage - Hands-On Lab Guide

💻 Windows Environment: All commands optimized for Windows PowerShell/Command Prompt.

⚠️ Prerequisites Check:

Day 12 complete (projects with tests created)
Java JDK 11+ and Maven installed
.NET SDK 6.0+ installed
Tests passing from Day 12
Azure DevOps pipeline configured

Lab 1: Add JaCoCo to Maven Project ☕

Objective: Configure JaCoCo for Java code coverage
Time: 25 minutes

Exercise 1.1: Configure JaCoCo Plugin

1 Open Your Maven Project

# Navigate to calculator project from Day 12
cd $env:USERPROFILE\Desktop\testing-demo\calculator

2 Update pom.xml with JaCoCo

notepad pom.xml

Add JaCoCo plugin to the <build><plugins> section:

<build>
    <plugins>
        <!-- Existing surefire plugin -->
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-surefire-plugin</artifactId>
            <version>3.0.0</version>
        </plugin>
        
        <!-- JaCoCo Coverage Plugin -->
        <plugin>
            <groupId>org.jacoco</groupId>
            <artifactId>jacoco-maven-plugin</artifactId>
            <version>0.8.11</version>
            <executions>
                <execution>
                    <id>prepare-agent</id>
                    <goals>
                        <goal>prepare-agent</goal>
                    </goals>
                </execution>
                <execution>
                    <id>report</id>
                    <phase>test</phase>
                    <goals>
                        <goal>report</goal>
                    </goals>
                </execution>
                <execution>
                    <id>check</id>
                    <goals>
                        <goal>check</goal>
                    </goals>
                    <configuration>
                        <rules>
                            <rule>
                                <element>BUNDLE</element>
                                <limits>
                                    <limit>
                                        <counter>LINE</counter>
                                        <value>COVEREDRATIO</value>
                                        <minimum>0.70</minimum>
                                    </limit>
                                </limits>
                            </rule>
                        </rules>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

Save and close (Ctrl+S, Alt+F4)

3 Understanding JaCoCo Configuration

Three Executions:

prepare-agent - Sets up coverage monitoring
report - Generates coverage report after tests
check - Enforces minimum coverage (70% in this example)

4 Run Tests with Coverage

# Run tests with coverage generation
mvn clean test

[INFO] --- jacoco:0.8.11:prepare-agent (prepare-agent) @ calculator ---
[INFO] --- maven-surefire-plugin:3.0.0:test (default-test) @ calculator ---
[INFO] Tests run: 8, Failures: 0, Errors: 0, Skipped: 0
[INFO] --- jacoco:0.8.11:report (report) @ calculator ---
[INFO] Loading execution data file: target\jacoco.exec
[INFO] Analyzed bundle 'calculator' with 1 classes
[INFO] BUILD SUCCESS

5 View Coverage Report

# Open HTML coverage report in browser
start target\site\jacoco\index.html

You'll see:

Overall coverage percentage
Coverage per package
Coverage per class
Green (covered) and red (uncovered) lines

✅ Checkpoint: JaCoCo configured and coverage report generated

Lab 2: Add Coverlet to .NET Project 🔷

Objective: Configure Coverlet for .NET code coverage
Time: 20 minutes

Exercise 2.1: Install Coverlet

1 Navigate to .NET Project

# Navigate to .NET solution from Day 12
cd $env:USERPROFILE\Desktop\testing-demo\CalculatorApp

2 Add Coverlet Package

# Add coverlet.collector to test project
dotnet add Calculator.Tests package coverlet.collector

info : PackageReference for package 'coverlet.collector' version '6.0.0' added
info : Committing restore...

# Alternative: Add coverlet.msbuild for more options
dotnet add Calculator.Tests package coverlet.msbuild

3 Run Tests with Coverage

# Collect coverage using XPlat Code Coverage
dotnet test --collect:"XPlat Code Coverage"

Passed!  - Failed:     0, Passed:    10, Skipped:     0, Total:    10, Duration: 52 ms

Attachments:
  C:\...\TestResults\abc-123\coverage.cobertura.xml

4 Generate HTML Report (Optional)

# Install ReportGenerator global tool
dotnet tool install -g dotnet-reportgenerator-globaltool

# Generate HTML report from coverage data
reportgenerator `
  -reports:"Calculator.Tests\TestResults\**\coverage.cobertura.xml" `
  -targetdir:"coveragereport" `
  -reporttypes:Html

# Open report
start coveragereport\index.html

5 View Coverage Details

In the HTML report, you'll see:

Summary: Overall coverage percentage
Assembly: Coverage per project
Classes: Coverage per class
Line-by-line: Green (covered) vs Red (uncovered)

✅ Checkpoint: Coverlet configured and coverage report generated

Lab 3: Improve Code Coverage 📈

Objective: Identify and test uncovered code
Time: 35 minutes

Exercise 3.1: Add Untested Method

1 Add New Method to Calculator (Java)

notepad src\main\java\com\example\Calculator.java

Add this method (no test yet):

public int modulo(int a, int b) {
    if (b == 0) {
        throw new IllegalArgumentException("Cannot modulo by zero");
    }
    return a % b;
}

Save and close

2 Run Coverage Without Test

mvn clean test
start target\site\jacoco\index.html

Observation: Coverage will be lower because modulo() method is not tested!

3 Add Test for New Method

notepad src\test\java\com\example\CalculatorTest.java

Add these tests:

    @Test
    @DisplayName("Test modulo operation")
    void testModulo() {
        assertEquals(1, calculator.modulo(7, 3));
        assertEquals(0, calculator.modulo(6, 3));
        assertEquals(2, calculator.modulo(8, 3));
    }
    
    @Test
    @DisplayName("Test modulo by zero throws exception")
    void testModulo_ByZero_ThrowsException() {
        Exception exception = assertThrows(
            IllegalArgumentException.class,
            () -> calculator.modulo(5, 0)
        );
        assertEquals("Cannot modulo by zero", exception.getMessage());
    }

Save and close

4 Run Coverage Again

mvn clean test
start target\site\jacoco\index.html

Observation: Coverage increases! modulo() method now shows green (covered)

5 Analyze Coverage Report

In the HTML report:

Click on package name → Click on Calculator class
See line-by-line coverage
Green background: Line was executed by tests ✅
Red background: Line never executed ❌
Yellow background: Partial branch coverage ⚠️

✅ Checkpoint: Understand how to improve coverage by adding tests

Lab 4: Add Coverage to Azure Pipeline (Maven) 🔗

Objective: Publish coverage reports to Azure DevOps
Time: 35 minutes

Exercise 4.1: Update Pipeline YAML

1 Open Pipeline File

notepad azure-pipelines.yml

2 Add Coverage Publishing

Replace content with complete pipeline:

# Maven Test + Coverage Pipeline

trigger:
  - main

pool:
  vmImage: 'windows-latest'

steps:
# Run tests with JaCoCo
- task: Maven@3
  displayName: 'Run Tests with Coverage'
  inputs:
    mavenPomFile: 'pom.xml'
    goals: 'clean test'
    publishJUnitResults: true
    testResultsFiles: '**/surefire-reports/TEST-*.xml'
    javaHomeOption: 'JDKVersion'
    jdkVersionOption: '1.11'

# Publish coverage results
- task: PublishCodeCoverageResults@2
  displayName: 'Publish Code Coverage'
  inputs:
    summaryFileLocation: '$(System.DefaultWorkingDirectory)/**/jacoco.xml'
    pathToSources: '$(System.DefaultWorkingDirectory)/src/main/java'
    codecoverageTool: 'JaCoCo'
    failIfCoverageEmpty: true

Save and close

3 Commit and Push

git add .
git commit -m "Add JaCoCo coverage to pipeline"
git push

4 Monitor Pipeline Execution

Go to Azure DevOps → Pipelines
Watch pipeline run
See "Publish Code Coverage" task execute
Pipeline completes successfully

5 View Coverage in Azure DevOps

In pipeline run, click "Code Coverage" tab
See coverage summary (e.g., 85.7%)
View coverage per file
Click files to see line-by-line coverage
Green = Covered, Red = Not covered

✅ Checkpoint: Coverage reports visible in Azure DevOps

Lab 5: Add Coverage to .NET Pipeline 🔷

Objective: Publish .NET coverage to Azure DevOps
Time: 30 minutes

Exercise 5.1: Update .NET Pipeline

1 Open Pipeline File

cd $env:USERPROFILE\Desktop\testing-demo\CalculatorApp
notepad azure-pipelines.yml

2 Complete .NET Coverage Pipeline

# .NET Test + Coverage Pipeline

trigger:
  - main

pool:
  vmImage: 'windows-latest'

steps:
# Restore packages
- task: DotNetCoreCLI@2
  displayName: 'Restore NuGet Packages'
  inputs:
    command: 'restore'

# Build
- task: DotNetCoreCLI@2
  displayName: 'Build Solution'
  inputs:
    command: 'build'
    arguments: '--configuration Release'

# Run tests with coverage
- task: DotNetCoreCLI@2
  displayName: 'Run Tests with Coverage'
  inputs:
    command: 'test'
    projects: '**/*Tests.csproj'
    arguments: '--configuration Release --collect:"XPlat Code Coverage"'
    publishTestResults: true

# Publish coverage results
- task: PublishCodeCoverageResults@2
  displayName: 'Publish Code Coverage'
  inputs:
    summaryFileLocation: '$(Agent.TempDirectory)/**/coverage.cobertura.xml'
    codecoverageTool: 'Cobertura'
    failIfCoverageEmpty: true

Save and close

3 Commit and Push

git add .
git commit -m "Add coverage to .NET pipeline"
git push

4 View .NET Coverage in Azure DevOps

Pipeline runs automatically
Click "Code Coverage" tab
See .NET project coverage
Drill down into assemblies and classes

✅ Checkpoint: .NET coverage integrated in pipeline

Lab 6: Enforce Coverage Thresholds 🚦

Objective: Fail builds when coverage drops below threshold
Time: 25 minutes

Exercise 6.1: Set Minimum Coverage (Maven)

1 Already Configured!

In Lab 1, we added the check execution with minimum 70%:

<limit>
    <counter>LINE</counter>
    <value>COVEREDRATIO</value>
    <minimum>0.70</minimum>
</limit>

2 Test Coverage Enforcement

Option A: Delete some tests to lower coverage

notepad src\test\java\com\example\CalculatorTest.java

Comment out 2-3 tests to reduce coverage below 70%

Run Maven:

mvn clean test

[ERROR] Coverage check failed:
Rule violated for bundle calculator: 
  lines covered ratio is 0.65, but expected minimum is 0.70
[INFO] BUILD FAILURE

3 Fix Coverage

Uncomment the tests or add more tests, then run again:

mvn clean test

[INFO] BUILD SUCCESS

Exercise 6.2: Coverage Threshold in Pipeline (Alternative)

1 Add BuildQualityChecks Task

Add after PublishCodeCoverageResults:

# Check coverage threshold
- task: BuildQualityChecks@8
  displayName: 'Check Coverage Threshold'
  inputs:
    checkCoverage: true
    coverageFailOption: 'build'
    coverageType: 'lines'
    coverageThreshold: '80'

💡 Note: BuildQualityChecks is from marketplace extension. JaCoCo's built-in check is simpler and recommended.

✅ Checkpoint: Coverage thresholds enforce quality standards

Lab 7: Track Coverage Trends 📈

Objective: Monitor coverage improvements over time
Time: 20 minutes

Exercise 7.1: View Coverage History

1 Access Analytics

Go to Azure DevOps → Pipelines
Select your pipeline
Click "Analytics" tab

2 View Coverage Trends

You can see:

Coverage percentage over time (line graph)
Increases and decreases highlighted
Compare coverage across builds
Identify when coverage dropped

3 Compare Build Coverage

Click on different pipeline runs
Compare Code Coverage tab
See which files improved/degraded

Exercise 7.2: Gradual Coverage Improvement

1 Strategy for Legacy Code

Don't aim for 80% immediately!

Gradual approach:

Week 1: Measure current coverage (e.g., 40%)
Week 2: Set goal at 45%, write tests
Week 4: Increase to 50%
Week 8: Reach 60%
Week 16: Target 80%

✅ Checkpoint: Understand coverage trends and improvement strategies

🎯 Lab Summary

What You've Accomplished:

✅ Configured JaCoCo for Java projects
✅ Configured Coverlet for .NET projects
✅ Generated coverage reports locally
✅ Published coverage to Azure DevOps
✅ Set coverage thresholds
✅ Viewed coverage trends
✅ Improved coverage by adding tests

Key Concepts Mastered:

Code Coverage: Percentage of code tested
JaCoCo: Java coverage tool with Maven integration
Coverlet: .NET coverage tool
Coverage Reports: HTML, XML formats
Thresholds: Minimum coverage enforcement
Trends: Tracking coverage over time

Next Steps:

📚 Day 14: Advanced test reporting and artifacts
🎯 Aim to increase coverage to 80%+
📊 Review coverage reports weekly
🧪 Add tests for uncovered critical code
📈 Track coverage in team dashboards

🔧 Troubleshooting Guide

Issue	Solution
No jacoco.xml generated	Verify JaCoCo plugin in pom.xml Check `target/site/jacoco/` directory exists Run: `mvn clean test`
Coverage shows 0%	Ensure tests actually ran and passed Check jacoco.exec file exists in target/ Verify source path is correct
Coverage not in Azure DevOps	Verify PublishCodeCoverageResults task added Check summaryFileLocation path is correct Ensure codecoverageTool matches (JaCoCo or Cobertura)
.NET coverage file not found	Check coverlet.collector package installed Use: `--collect:"XPlat Code Coverage"` Look in: `TestResults/**/coverage.cobertura.xml`
Build fails on coverage check	Coverage below minimum threshold Add more tests or lower threshold temporarily Review uncovered code in report

📝 Quick Reference Commands

Maven / JaCoCo:

# Run tests with coverage
mvn clean test

# View coverage report
start target\site\jacoco\index.html

# Check coverage threshold
mvn clean verify
# Fails if below minimum

.NET / Coverlet:

# Run tests with coverage
dotnet test --collect:"XPlat Code Coverage"

# Generate HTML report
reportgenerator `
  -reports:"**/coverage.cobertura.xml" `
  -targetdir:"coveragereport" `
  -reporttypes:Html

# View report
start coveragereport\index.html

Coverage Files:

# Maven/JaCoCo
target\site\jacoco\index.html     # HTML report
target\site\jacoco\jacoco.xml     # XML for tools
target\jacoco.exec                # Raw execution data

# .NET/Coverlet
TestResults\{guid}\coverage.cobertura.xml  # Coverage data
coveragereport\index.html                   # HTML (if using reportgenerator)

🎉 Day 13 Labs Complete!

You've successfully implemented code coverage tracking!

Ready for Day 14: Advanced Test Reporting & Artifacts

🎓 Skills Acquired:

JaCoCo configuration and usage
Coverlet configuration for .NET
Coverage report generation
Coverage publishing to Azure DevOps
Setting and enforcing thresholds
Coverage trend analysis

📊 Day 13: Code Coverage - Hands-On Lab Guide

Lab 1: Add JaCoCo to Maven Project ☕

Exercise 1.1: Configure JaCoCo Plugin

Lab 2: Add Coverlet to .NET Project 🔷

Exercise 2.1: Install Coverlet

Lab 3: Improve Code Coverage 📈

Exercise 3.1: Add Untested Method

Lab 4: Add Coverage to Azure Pipeline (Maven) 🔗

Exercise 4.1: Update Pipeline YAML

Lab 5: Add Coverage to .NET Pipeline 🔷

Exercise 5.1: Update .NET Pipeline

Lab 6: Enforce Coverage Thresholds 🚦

Exercise 6.1: Set Minimum Coverage (Maven)

Exercise 6.2: Coverage Threshold in Pipeline (Alternative)

Lab 7: Track Coverage Trends 📈

Exercise 7.1: View Coverage History

Exercise 7.2: Gradual Coverage Improvement

🎯 Lab Summary

What You've Accomplished:

Key Concepts Mastered:

Next Steps:

🔧 Troubleshooting Guide

📝 Quick Reference Commands

Maven / JaCoCo:

.NET / Coverlet:

Coverage Files:

🎉 Day 13 Labs Complete!