RxJava2 FlatMap,SwitchMap,ConcatMap TestCases in Kotlin

RxJava2UnitTest.java

import io.reactivex.Observable
import io.reactivex.schedulers.TestScheduler
import org.junit.Test
import java.util.*
import java.util.concurrent.TimeUnit

class ExampleUnitTest {

    @Test
    @Throws(Exception::class)
    fun flatMap() {

        val scheduler = TestScheduler()

        val delay = 100L

        Observable.fromIterable(listOf("a", "b", "c", "d", "e", "f"))
                .flatMap {
                    Observable.just(it + "x")
                }
                .delaySubscription(delay, TimeUnit.SECONDS, scheduler)
                .filter { it.contains("c") }
                .doOnNext() {
                    print("flatMap: ${it} \n")
                }
                .subscribe()

        scheduler.advanceTimeBy(200, TimeUnit.SECONDS)
    }
    
    //Expected Result: cx

    @Test
    @Throws(Exception::class)
    fun switchMap() {

        val scheduler = TestScheduler()

        Observable.fromIterable(listOf("a", "b", "c", "d", "e", "f"))
                .switchMap({ s ->
                    val delay = Random().nextInt(10)
                    Observable.just<String>(s + "x")
                            .delay(delay.toLong(), TimeUnit.SECONDS, scheduler)
                })
                .filter { it.contains("c") }
                .doAfterNext {
                    print("switchMap: ${it}\n")
                }
                .subscribe()

        scheduler.advanceTimeBy(1, TimeUnit.MINUTES)
    }
    
    //Expected Result: Empty

    @Test
    @Throws(Exception::class)
    fun concatMap() {

        val scheduler = TestScheduler()

        Observable.fromIterable(listOf("a", "b", "c", "d", "e", "f"))
                .concatMap({ s ->
                    val delay = Random().nextInt(10)
                    Observable.just<String>(s + "x")
                            .delay(delay.toLong(), TimeUnit.SECONDS, scheduler)
                })
                .filter { it.contains("c") }
                .doAfterNext {
                    print("concatMap: ${it}\n")
                }
                .subscribe()

        scheduler.advanceTimeBy(1, TimeUnit.MINUTES)
    }
    
    //Expected Result: cx
}