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?

score 23 · Accepted Answer · answered May 22 '17 at 13:55

23

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)

answered May 22 '17 at 13:55

Cyrille Corpet

5,265
1
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31

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. – rabejens May 22 '17 at 13:57
Glad I could help. I find this really helpful, since you can use it for different error handling contexts. – Cyrille Corpet May 22 '17 at 14:06
How to check for failure? – Jus12 Feb 16 '19 at 15:54
2

`maybeRes.failure.exception should have message "/ by zero"`, see the [scaladoc](http://doc.scalatest.org/3.0.0/index.html#org.scalatest.TryValues) – Cyrille Corpet Feb 16 '19 at 21:38

score 12 · Answer 2 · answered May 22 '17 at 12:28

12

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

maybeRes shouldBe Success("moo")

answered May 22 '17 at 12:28

Matt Fowler

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@rabejens 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. – flavian May 22 '17 at 13:56
@flavian that's why I marked Cyrille Corpet's answer as the correct one. – rabejens May 22 '17 at 14:53
1

Unfortunate that scalatest doesn't support this as the best answer. Clearly this is a simpler semantic than dealing with TryValues. – Courtland Caldwell Apr 05 '18 at 16:33

score 2 · Answer 3 · answered May 22 '17 at 13:50

2

Alternatively

import org.scalatest.TryValues._

// ... 

maybeRes.success.value should be "moo"

answered May 22 '17 at 13:50

Gabriele Petronella

106,943
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score 1 · Answer 4 · answered Apr 29 '22 at 02:52

1

I cannot find anything like should be(successful).

maybeRes must be a 'success

answered Apr 29 '22 at 02:52

Laurent

107
7

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

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