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This sample shows how to test Java projects with JaCoCo in Gradle.

To collect code coverage across multiple subprojects, we need to setup two aspects. First, the projects that run the tests and collect the code coverage data:

buildSrc/src/main/groovy/myproject.java-conventions.gradle
plugins {
    id 'java'
    id 'jacoco'
}

version = '1.0.2'
group = 'org.gradle.sample'

repositories {
    mavenCentral()
}

tasks.named("test") {
    useJUnitPlatform()
}

dependencies {
    testImplementation 'org.junit.jupiter:junit-jupiter:5.7.1'
}

// Do not generate reports for individual projects
tasks.named("jacocoTestReport") {
    enabled = false
}

// Share sources folder with other projects for aggregated JaCoCo reports
configurations.create('transitiveSourcesElements') {
    visible = false
    canBeResolved = false
    canBeConsumed = true
    extendsFrom(configurations.implementation)
    attributes {
        attribute(Usage.USAGE_ATTRIBUTE, objects.named(Usage, Usage.JAVA_RUNTIME))
        attribute(Category.CATEGORY_ATTRIBUTE, objects.named(Category, Category.DOCUMENTATION))
        attribute(DocsType.DOCS_TYPE_ATTRIBUTE, objects.named(DocsType, 'source-folders'))
    }
    sourceSets.main.java.srcDirs.forEach {
        outgoing.artifact(it)
    }
}

// Share the coverage data to be aggregated for the whole product
configurations.create('coverageDataElements') {
    visible = false
    canBeResolved = false
    canBeConsumed = true
    extendsFrom(configurations.implementation)
    attributes {
        attribute(Usage.USAGE_ATTRIBUTE, objects.named(Usage, Usage.JAVA_RUNTIME))
        attribute(Category.CATEGORY_ATTRIBUTE, objects.named(Category, Category.DOCUMENTATION))
        attribute(DocsType.DOCS_TYPE_ATTRIBUTE, objects.named(DocsType, 'jacoco-coverage-data'))
    }
    // This will cause the test task to run if the coverage data is requested by the aggregation task
    outgoing.artifact(tasks.named("test").map { task ->
        task.extensions.getByType(JacocoTaskExtension).destinationFile
    })
}
buildSrc/src/main/kotlin/myproject.java-conventions.gradle.kts
plugins {
    java
    jacoco
}

version = "1.0.2"
group = "org.gradle.sample"

repositories {
    mavenCentral()
}

tasks.test {
    useJUnitPlatform()
}

dependencies {
    testImplementation("org.junit.jupiter:junit-jupiter:5.7.1")
}

// Do not generate reports for individual projects
tasks.jacocoTestReport {
    enabled = false
}

// Share sources folder with other projects for aggregated JaCoCo reports
configurations.create("transitiveSourcesElements") {
    isVisible = false
    isCanBeResolved = false
    isCanBeConsumed = true
    extendsFrom(configurations.implementation.get())
    attributes {
        attribute(Usage.USAGE_ATTRIBUTE, objects.named(Usage.JAVA_RUNTIME))
        attribute(Category.CATEGORY_ATTRIBUTE, objects.named(Category.DOCUMENTATION))
        attribute(DocsType.DOCS_TYPE_ATTRIBUTE, objects.named("source-folders"))
    }
    sourceSets.main.get().java.srcDirs.forEach {
        outgoing.artifact(it)
    }
}

// Share the coverage data to be aggregated for the whole product
configurations.create("coverageDataElements") {
    isVisible = false
    isCanBeResolved = false
    isCanBeConsumed = true
    extendsFrom(configurations.implementation.get())
    attributes {
        attribute(Usage.USAGE_ATTRIBUTE, objects.named(Usage.JAVA_RUNTIME))
        attribute(Category.CATEGORY_ATTRIBUTE, objects.named(Category.DOCUMENTATION))
        attribute(DocsType.DOCS_TYPE_ATTRIBUTE, objects.named("jacoco-coverage-data"))
    }
    // This will cause the test task to run if the coverage data is requested by the aggregation task
    outgoing.artifact(tasks.test.map { task ->
        task.extensions.getByType<JacocoTaskExtension>().destinationFile!!
    })
}

Here we do the setup in a convention plugin called myproject.java-conventions which we apply to all our application and library projects. Here, the build is setup to run tests using JUnit5 and we apply the jacoco plugin to collect the code coverage. With the plugin applied, it automatically attaches itself to the test task to collect the code coverage. Please refer to the JaCoCo chapter for more details on the plugin configuration.

Second, to generate a report spanning all our tested projects, we introduce and additional project code-coverage-report that collects source files and coverage data from all its dependent projects. This is setup in a second convention plugin plugin called myproject.jacoco-aggregation which provides a task called codeCoverageReport to generate the aggregated report.

buildSrc/src/main/groovy/myproject.jacoco-aggregation.gradle
plugins {
    id 'java'
    id 'jacoco'
}

repositories {
    mavenCentral()
}

// A resolvable configuration to collect source code
def sourcesPath = configurations.create("sourcesPath") {
    visible = false
    canBeResolved = true
    canBeConsumed = false
    extendsFrom(configurations.implementation)
    attributes {
        attribute(Usage.USAGE_ATTRIBUTE, objects.named(Usage, Usage.JAVA_RUNTIME))
        attribute(Category.CATEGORY_ATTRIBUTE, objects.named(Category, Category.DOCUMENTATION))
        attribute(DocsType.DOCS_TYPE_ATTRIBUTE, objects.named(DocsType, 'source-folders'))
    }
}

// A resolvable configuration to collect JaCoCo coverage data
def coverageDataPath = configurations.create("coverageDataPath") {
    visible = false
    canBeResolved = true
    canBeConsumed = false
    extendsFrom(configurations.implementation)
    attributes {
        attribute(Usage.USAGE_ATTRIBUTE, objects.named(Usage, Usage.JAVA_RUNTIME))
        attribute(Category.CATEGORY_ATTRIBUTE, objects.named(Category, Category.DOCUMENTATION))
        attribute(DocsType.DOCS_TYPE_ATTRIBUTE, objects.named(DocsType, 'jacoco-coverage-data'))
    }
}

// Task to gather code coverage from multiple subprojects
def codeCoverageReport = tasks.register('codeCoverageReport', JacocoReport) {
    additionalClassDirs(configurations.runtimeClasspath)
    additionalSourceDirs(sourcesPath.incoming.artifactView { lenient(true) }.files)
    executionData(coverageDataPath.incoming.artifactView { lenient(true) }.files.filter { it.exists() })

    reports {
        // xml is usually used to integrate code coverage with
        // other tools like SonarQube, Coveralls or Codecov
        xml.required = true

        // HTML reports can be used to see code coverage
        // without any external tools
        html.required = true
    }
}

// Make JaCoCo report generation part of the 'check' lifecycle phase
tasks.named("check") {
    dependsOn(codeCoverageReport)
}
buildSrc/src/main/kotlin/myproject.jacoco-aggregation.gradle.kts
plugins {
    java
    jacoco
}

repositories {
    mavenCentral()
}

// A resolvable configuration to collect source code
val sourcesPath: Configuration by configurations.creating {
    isVisible = false
    isCanBeResolved = true
    isCanBeConsumed = false
    extendsFrom(configurations.implementation.get())
    attributes {
        attribute(Usage.USAGE_ATTRIBUTE, objects.named(Usage.JAVA_RUNTIME))
        attribute(Category.CATEGORY_ATTRIBUTE, objects.named(Category.DOCUMENTATION))
        attribute(DocsType.DOCS_TYPE_ATTRIBUTE, objects.named("source-folders"))
    }
}

// A resolvable configuration to collect JaCoCo coverage data
val coverageDataPath: Configuration by configurations.creating {
    isVisible = false
    isCanBeResolved = true
    isCanBeConsumed = false
    extendsFrom(configurations.implementation.get())
    attributes {
        attribute(Usage.USAGE_ATTRIBUTE, objects.named(Usage.JAVA_RUNTIME))
        attribute(Category.CATEGORY_ATTRIBUTE, objects.named(Category.DOCUMENTATION))
        attribute(DocsType.DOCS_TYPE_ATTRIBUTE, objects.named("jacoco-coverage-data"))
    }
}

// Task to gather code coverage from multiple subprojects
val codeCoverageReport by tasks.registering(JacocoReport::class) {
    additionalClassDirs(configurations.runtimeClasspath.get())
    additionalSourceDirs(sourcesPath.incoming.artifactView { lenient(true) }.files)
    executionData(coverageDataPath.incoming.artifactView { lenient(true) }.files.filter { it.exists() })

    reports {
        // xml is usually used to integrate code coverage with
        // other tools like SonarQube, Coveralls or Codecov
        xml.required.set(true)

        // HTML reports can be used to see code coverage
        // without any external tools
        html.required.set(true)
    }
}

// Make JaCoCo report generation part of the 'check' lifecycle phase
tasks.check {
    dependsOn(codeCoverageReport)
}

Running the tests and generate the report:

$ ./gradlew codeCoverageReport

BUILD SUCCESSFUL
11 actionable tasks: 11 executed

For more information, see Testing in Java project chapter.