How to test a Try[T] with ScalaTest correctly?

Question

I have a method that returns a Try object:

def doSomething(p: SomeParam): Try[Something] = {
  // code
}

I now want to test this with ScalaTest. Currently I am doing it like this:

"My try method" should "succeed" in {
  val maybeRes = doSomething(SomeParam("foo"))
  maybeRes.isSuccess shouldBe true
  val res = maybeRes.get
  res.bar shouldBe "moo"
}

However checking for isSuccess to be true looks a bit clumsy because for Options and Sequences there are things like should be(empty) and shouldNot be(empty). I cannot find anything like should be(successful).

Does this exist or is my approach really the way to go?

Largo

Answer 1

Another possibility is to do

import org.scalatest.TryValues._
maybeRes.success.value.bar shouldBe "moo"

This will give a message indicating the Try was not a success, instead of throwing the exception in maybeRes.get.

The analog exist for Option, Either and PartialFunction (using the relevant import)

Pirtle

This was what I really looked for - testing for success and getting the result object (which is not only a string in my real code) for further tests. – Largo

Glad I could help. I find this really helpful, since you can use it for different error handling contexts. – Pirtle

How to check for failure? – Manilla

maybeRes.failure.exception should have message "/ by zero", see the scaladoc – Pirtle

Answer 2

Just check to see that it is the success type with your return value:

maybeRes shouldBe Success("moo")

Anastassia

@Largo The correct way which lets failed try errors propagate in the ScalaTest reporting pipeline is maybeRes.success.value shouldBe "moo", and you get that by mixing in TryValues. The answer above is wrong, because there's reporting precision loss when you intentionally hide the error. – Trapezius

@Trapezius that's why I marked Cyrille Corpet's answer as the correct one. – Largo

Unfortunate that scalatest doesn't support this as the best answer. Clearly this is a simpler semantic than dealing with TryValues. – Lipo

Answer 3

Alternatively

import org.scalatest.TryValues._

// ... 

maybeRes.success.value should be "moo"

Carrousel

Answer 4

I cannot find anything like should be(successful).

maybeRes must be a 'success

Satiny