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

I am 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)
}

      

        
        
        
      

    

In case the .observeOn(AndroidSchedulers.mainThread())

test blocks are infinitely on returnedObservable.toBlocking().first()

.

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

returnedObservable

returned from a method call using .subscribeOn and .observeOn, so removing those parameters is not an option.