aggregating gradle multiproject test results using TestReport

From Example 4. Creating a unit test report for subprojects in the Gradle User Guide:

subprojects {
    apply plugin: 'java'

    // Disable the test report for the individual test task
    test {
        reports.html.enabled = false
    }
}

task testReport(type: TestReport) {
    destinationDir = file("$buildDir/reports/allTests")
    // Include the results from the `test` task in all subprojects
    reportOn subprojects*.test
}

Fully working sample is available from samples/testing/testReport in the full Gradle distribution.

If using kotlin Gradle DSL

val testReport = tasks.register<TestReport>("testReport") {
    destinationDir = file("$buildDir/reports/tests/test")
    reportOn(subprojects.map { it.tasks.findByPath("test") })

subprojects {
    tasks.withType<Test> {
        useJUnitPlatform()
        finalizedBy(testReport)
        ignoreFailures = true
        testLogging {
            events("passed", "skipped", "failed")
        }
    }
}

And execute gradle testReport. Source How to generate an aggregated test report for all Gradle subprojects

In addition to the subprojects block and testReport task suggested by @peter-niederwieser above, I would add another line to the build below those:

tasks('test').finalizedBy(testReport)

That way if you run gradle test (or even gradle build), the testReport task will run after the subproject tests complete. Note that you have to use tasks('test') rather than just test.finalizedBy(...) because the test task doesn't exist in the root project.