Java Coverage

JaCoCo code coverage configuration for Java/Gradle projects.

When to use this skill

Setting up code coverage reporting
Configuring coverage thresholds
Aggregating coverage across modules
Integrating with SonarQube
Troubleshooting coverage reports
When asked to "improve test coverage"

Skill Contents

Sections

When to use this skill (L23-L31)
Quick Start (L57-L94)
Coverage Thresholds (L95-L119)
Exclusions (L120-L139)
Multi-Module Aggregation (L140-L190)
SonarQube Integration (L191-L201)
References (L202-L208)
Related Rules (L209-L212)
Related Skills (L213-L219)

Available Resources

📚 references/ - Detailed documentation

Quick Start

1. Apply JaCoCo Plugin

plugins {
    id 'jacoco'
}

jacoco {
    toolVersion = "0.8.14"
}

2. Configure Report Task

jacocoTestReport {
    dependsOn test

    reports {
        xml.required = true  // For SonarQube
        html.required = true // For local viewing
    }
}

test {
    finalizedBy jacocoTestReport
}

3. Run Coverage

./gradlew test jacocoTestReport
# Report at: build/reports/jacoco/test/html/index.html

Coverage Thresholds

jacocoTestCoverageVerification {
    violationRules {
        rule {
            limit {
                minimum = 0.80  // 80% minimum coverage
            }
        }

        rule {
            element = 'CLASS'
            excludes = ['*.generated.*', '*.config.*']
            limit {
                counter = 'LINE'
                minimum = 0.70
            }
        }
    }
}

check.dependsOn jacocoTestCoverageVerification

Exclusions

Common patterns to exclude from coverage:

jacocoTestReport {
    afterEvaluate {
        classDirectories.setFrom(files(classDirectories.files.collect {
            fileTree(dir: it, exclude: [
                '**/generated/**',
                '**/config/**',
                '**/*Config.class',
                '**/*Properties.class',
                '**/Application.class'
            ])
        }))
    }
}

Multi-Module Aggregation

For aggregated reports across modules, use the modern jacoco-report-aggregation plugin (Gradle 7.4+):

// In root build.gradle
plugins {
    id 'base'
    id 'jacoco-report-aggregation'
}

// Ensure subprojects are evaluated first
subprojects.each { evaluationDependsOn(it.path) }

dependencies {
    subprojects.each { jacocoAggregation it }
}

reporting {
    reports {
        testCodeCoverageReport(JacocoCoverageReport) {
            testType = TestSuiteType.UNIT_TEST
        }
    }
}

For older Gradle versions, use a manual task with defensive filtering:

// In root build.gradle (Gradle < 7.4)
task jacocoRootReport(type: JacocoReport) {
    dependsOn subprojects*.test

    // Use defensive filtering to avoid missing-directory errors
    def srcDirs = files(subprojects*.sourceSets*.main*.allSource*.srcDirs).filter { it.exists() }
    def classDirs = files(subprojects*.sourceSets*.main*.output).filter { it.exists() }
    def execData = files(subprojects*.jacocoTestReport*.executionData).filter { it.exists() }

    additionalSourceDirs.from(srcDirs)
    sourceDirectories.from(srcDirs)
    classDirectories.from(classDirs)
    executionData.from(execData)

    reports {
        xml.required = true
        html.required = true
    }
}

SonarQube Integration

sonar {
    properties {
        property 'sonar.coverage.jacoco.xmlReportPaths',
            "${projectDir}/build/reports/jacoco/test/jacocoTestReport.xml"
    }
}

References

| Reference | Description | |-----------|-------------| | references/exclusion-patterns.md | Common exclusion patterns | | references/multi-module.md | Multi-module aggregation |

Related Rules

java-jacoco-coverage - Full JaCoCo reference

Related Skills

| Skill | Purpose | |-------|---------| | java-testing | Test configuration | | fix-sonarqube | SonarQube setup | | gradle-standards | Gradle configuration |