Android JUnit test blocks indefinitely when Observable observed on AndroidSchedulers.mainThread()

Question

I'm writing a simple test that is equivalent to:

Test fun testObservable() {
    val returnedObservable = Observable.create(object : Observable.OnSubscribe<String> {
        override fun call(t: Subscriber<in String>) {
            t.onNext("hello")
            t.onCompleted()
        }

    }).subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())

    val result = returnedObservable.toBlocking().first()
    assertEquals("hello", result)
}

The test blocks indefinitely on returnedObservable.toBlocking().first() when .observeOn(AndroidSchedulers.mainThread()) is present.

Is there a way to transform the observable to return the result?

The returnedObservable is returned from method call with .subscribeOn and .observeOn already applied so removing those is not an option.

Answer 1

I guess it is a bug mentioned here: https://github.com/ReactiveX/RxAndroid/issues/50

btw why don't you use RxKotlin?

You example will look much better:

    val returnedObservable = observable<String> { subscriber ->
        subscriber.onNext("hello")
        subscriber.onCompleted()
    }
    .subscribeOn(Schedules.io())
    .observeOn(AndroidSchedulers.mainThread())