build.gradle

plugins {
    id 'application'
    id 'java'
}

group = 'io.testable'
version = '1.0-SNAPSHOT'

repositories {
    mavenCentral()
}

dependencies {
    testImplementation 'junit:junit:4.13.2'
    testImplementation 'org.testng:testng:6.14.3'
}

application {

    mainClass = 'io.testable.example.MainSampleTest'
}

tasks.named('test') {
    if (Boolean.getBoolean("isTestNG"))
        useTestNG()
    else
        useJUnit()
}

tasks.register('uberTestJar', Jar) {
    dependsOn testClasses
    manifest {
        attributes 'Main-Class': 'io.testable.example.MainSampleTest'
    }
    sourceSets.main.output.each {
        from it
    }
    sourceSets.test.output.each {
        from it
    }
    from { configurations.runtimeClasspath.collect { it.isDirectory() ? it : zipTree(it) } }
    from { configurations.testRuntimeClasspath.collect { it.isDirectory() ? it : zipTree(it) } }
    with jar
}