mongo-scala-driver: 4.3.1

exceptions thrown in map or flatmap for Observable are not propagated up.

take for example

val obs: Future[Unit] =
  (for {
      _ <- collection.insert(BsonDocument())
      _ = sys.error("Boom")
    } yield ()
   ).toFuture()

this future will never complete and lead to a timeout.

Only exceptions thrown in an Observable are propagated up. e.g. using a `raiseError` defined as such

def raiseError[A](e: Throwable) = new Observable[A] {
  val delegate: Observable[Unit] = Observable[Unit](Seq(()))
     override def subscribe(observer: Observer[_ >: A]): Unit =
       delegate.subscribe(
         new Observer[Unit] {
           override def onError(throwable: Throwable): Unit =
             observer.onError(throwable)

          override def onSubscribe(sub: Subscription): Unit =
             observer.onSubscribe(sub)

          override def onComplete(): Unit =
             () // not reached

          override def onNext(tResult: Unit): Unit =
             onError(e)
         }
       )
  }

It would seem resolvable by changing `onNext` in MapObservable  to

override def onNext(tResult: T): Unit =
  try {
     observer.onNext(s(tResult))
   } catch {
     case t: Throwable => observer.onError(f(t))
   }

and FlatMapObservable similarly.