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