How to check an "Either" result in Scala Test?

Question

I am relatively new to Scala Test, and so I consulted the documentation on how to test on Either values.

I tried to replicate the instructions like that:

import org.scalatest.EitherValues
import org.scalatest.flatspec.AnyFlatSpec

class EitherTest extends AnyFlatSpec with EitherValues {
  val either: Either[Exception, Int] = Right(42)

  either.right.value should be > 1
}

This implementation does not do the trick, I get a syntax error. What did I do wrong?

Error:

Error:(9, 22) value should is not a member of Int either.right.value should be > 1 Error:(9, 29) not found: value be either.right.value should be > 1 – Hannes 14 hours ago

Answer 1

Testing Either by matching with pattern can be more readable. ScalaTest's Inside trait allows you to make assertions after a pattern match.

import org.scalatest.Inside
import org.scalatest.flatspec.AnyFlatSpec
import org.scalatest.matchers.should.Matchers

class EitherTest extends AnyFlatSpec with Inside with Matchers {
  val either: Either[Exception, Int] = Right(42)

  either should matchPattern { case Right(42) => }

  inside(either) { case Right(n) =>
    n should be > 1
  }

  val either2: Either[Exception, Int] = Left(new Exception("Bad argument"))

  inside(either2) { case Left(e) =>
    e.getMessage should startWith ("Bad")
  }

}