You can open this sample in an IDE that supports Gradle.

This sample shows how to aggregate code coverage across multiple Java subprojects using JaCoCo. The jacoco-report-aggregation plugin provides this ability via a standalone project used to specify which subprojects to include for aggregation.

The project in this example contains three "code" subprojects: application, list and utilities. All three projects apply the jacoco plugin, and application consumes both list and utilities via its implementation configuration. A fourth subproject code-coverage-report is the standalone utility project used to collect the coverage results.

The Test Report Aggregation plugin does not currently work with the com.android.application plugin.
code-coverage-report/build.gradle.kts
plugins {
    base
    id("jacoco-report-aggregation")
}

repositories {
    mavenCentral()
}

dependencies {
    jacocoAggregation(project(":application")) (1)
}

reporting {
    reports {
        val testCodeCoverageReport by creating(JacocoCoverageReport::class) { (2)
            testType = TestSuiteType.UNIT_TEST
        }
    }
}

tasks.check {
    dependsOn(tasks.named<JacocoReport>("testCodeCoverageReport")) (3)
}
code-coverage-report/build.gradle
plugins {
    id 'base'
    id 'jacoco-report-aggregation'
}

repositories {
    mavenCentral()
}

dependencies {
    jacocoAggregation project(':application') (1)
}

reporting {
    reports {
        testCodeCoverageReport(JacocoCoverageReport) { (2)
            testType = TestSuiteType.UNIT_TEST
        }
    }
}

tasks.named('check') {
    dependsOn tasks.named('testCodeCoverageReport', JacocoReport) (3)
}

The standalone project applies jacoco-report-aggregation, but requires additional configuration if the jvm-test-suite plugin is not also present.

In this scenario, two additional pieces of setup are necessary:

1 Declare dependencies using the jacocoAggregation configuration
2 Define a report of type JacocoCoverageReport which collects coverage data from unit test suites
3 Optional: make JaCoCo aggregate report generation part of the 'check' lifecycle phase

The report aggregation logic does not automatically inspect all subprojects for coverage data to aggregate. Instead, the direct and transitive project dependencies of the jacocoAggregation configuration are selected for potential aggregation.

The user must also declare one or more reports of type JacocoCoverageReport. Each report instance specifies a testType property, used to match the test suite producing the coverage data. A JacocoReport task is synthesized for each user-defined report and performs the aggregation. Invoking this task will cause tests to be executed in the dependent projects of the jacocoAggregation configuration.

Running the tests and generate the report:

$ ./gradlew testCodeCoverageReport

BUILD SUCCESSFUL
25 actionable tasks: 25 executed

XML and HTML reports can now be found under code-coverage-report/build/reports/jacoco/testCodeCoverageReport.

For more information, see Testing in Java project chapter.