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

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"
    }
}

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

java-coverage