java-coverage

name	java-coverage
description	JaCoCo code coverage configuration for Java/Gradle projects. Covers report generation, coverage thresholds, multi-module aggregation, and SonarQube integration. Use when setting up or troubleshooting code coverage.
compatibility	Java projects using Gradle with JaCoCo plugin
metadata	{"version":"2.0.0","technology":"java","category":"quality","tags":["java","jacoco","coverage","testing"]}

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
• Quick Start
• Coverage Thresholds
• Exclusions
• Multi-Module Aggregation
• SonarQube Integration
• Checking Coverage via SonarQube MCP
• References
• Related Rules
• Related Skills

Available Resources

references/ - Detailed documentation

• coverage targets
• coverage via mcp
• exclusion patterns
• improvement workflow
• multi module
• prioritization

---

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"
    }
}

Checking Coverage via SonarQube MCP

Instead of running local JaCoCo builds to check current coverage state, use SonarQube MCP tools for faster feedback:

Tool	Purpose
search_files_by_coverage	Find files with lowest coverage
get_file_coverage_details	Line-by-line coverage for a specific file
get_component_measures	Project/module-level coverage metric
get_project_quality_gate_status	Check if coverage gate passes

# Find low-coverage files
search_files_by_coverage: projectKey: "my-service"

# Check specific file coverage
get_file_coverage_details: key: "my-service:src/main/java/com/bitso/Service.java"

# Check overall coverage
get_component_measures: component: "my-service", metricKeys: ["coverage"]

MCP reflects the last CI analysis. Use JaCoCo locally to generate new coverage after writing tests.

See fix-sonarqube coverage reference for the full MCP coverage workflow.

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