scalatest intercept vs a[Exception] should be thrownBy

Question

I'm testing some Future that fails, and I tried it in two different ways, one that works:

intercept[NoSuchElementException] {
  Await.result(dao.findById("some_id"), Duration.Inf)
}

and one that dosen't:

a[NoSuchElementException] should be thrownBy dao.findById("some_id")

It happened to me before, and I'm trying to figure out why is that..?

Would love to get some help understanding this.

findById simply throws NoSuchElementException if it fails:

  def findById(id: String): Future[Person] = {
    collection.find(json(Vendor.PersonId -> id))
      .requireOne[Person] recover {
      case NoSuchResultException => throw new NoSuchElementException
    }
  }

Answer 1

The problem you are facing is that the Future is not handle correctly.

Given this definition:

def findById(id: String): Future[Person] = {
  collection.find(json(Vendor.PersonId -> id))
    .requireOne[Person] recover {
     case NoSuchResultException => throw new NoSuchElementException
    }
}

the recover will map a NoSuchResultException into a throw new NoSuchElementException, but it always wrapped inside the Future.

This means that returned object will be a failed Future and the method won't throw any exception.

To handle such case you could, for example, mix-in your test class with the ScalaFutures trait in scalatest. This helps you to handle the future like

dao.findById("some_id").failed.futureValue should be a[NoSuchElementException]