functionalTestRuntimeOnly.extendsFrom testRuntimeOnly
            }

            task functionalTest(type: Test) {
                useJUnitPlatform()
                testClassesDirs = sourceSets.functionalTest.output.classesDirs
                classpath = sourceSets.functionalTest.runtimeClasspath
            }

            gradlePlugin {
                testSourceSets sourceSets.functionalTest

            $junitSetup
            tasks.register('otherTests', Test) {
                binaryResultsDirectory = file("bin")
                classpath = files('blahClasspath')
                testClassesDirs = files("blah")
            }
            tasks.register('testReport', TestReport) {
                reportOn test, otherTests
                destinationDir reporting.file("tr")
            }
        """

            test.${configureTestFramework}

            task test2(type: Test) {
                ${configureTestFramework}
                classpath = sourceSets.test2.runtimeClasspath
                testClassesDirs = sourceSets.test2.output.classesDirs
            }

            check {
                dependsOn test2
            }

            dependencies {

            BuildScriptBuilder.Expression functionalTest = buildScriptBuilder.taskRegistration("Add a task to run the functional tests", "functionalTest", "Test", b -> {
                b.propertyAssignment(null, "testClassesDirs", buildScriptBuilder.propertyExpression(functionalTestSourceSet, "output.classesDirs"), true);

Tasks are units of work executed during your build.
They can be defined by plugins or inline:

[.multi-language-sample]
=====
[source, kotlin]
----
val functionalTest by tasks.registering(Test::class) {
    testClassesDirs = functionalTestSourceSet.output.classesDirs
    classpath = functionalTestSourceSet.runtimeClasspath
    useJUnitPlatform()
}

tasks.named<Test>("test") {
    // Use JUnit Jupiter for unit tests.

                sourceCompatibility = "${compileJavaVersion}"
                targetCompatibility = "${compileJavaVersion}"
            }

            task test(type: Test) {
                testClassesDirs = buildDir.files("classes/java/test")
                classpath = files(configurations.testImplementation, buildDir.dir("classes/java/test"))
                binaryResultsDirectory.set(buildDir.dir("test-results"))

                    resources {
                        srcDir 'src/functional/resources'
                    }
                }
            }

            task functionalTest(type: Test) {
                testClassesDirs = sourceSets.functionalTest.output.classesDirs
                classpath = sourceSets.functionalTest.runtimeClasspath
            }

            check.dependsOn functionalTest

            gradlePlugin {

            tasks.register("mytest", Test) {
                // Must ensure a base dir is set here
                testClassesDirs = files(customClassesDir)
            }

            task assertNoTestClasses {
                inputs.files mytest.testClassesDirs

                doLast {
                    assert inputs.files.contains(customClassesDir)
                }
            }

        }
    }

    private
    fun Project.createGeneratePerformanceDefinitionJsonTask(name: String, performanceSourceSet: SourceSet, outputJson: File) =
        tasks.register<Test>(name) {
            testClassesDirs = performanceSourceSet.output.classesDirs
            classpath = performanceSourceSet.runtimeClasspath
            maxParallelForks = 1

        task.binaryResultsDirectory.set(task.project.file('build/test-results'))
        task.reports.junitXml.outputLocation.set(task.project.file('build/test-results'))
        task.testClassesDirs = task.project.layout.files()
    }

    def expectTestSuiteFails() {
        def testId = "test"
        suiteDescriptor.id >> testId
        suiteDescriptor.parent >> null