Matcher is only as good as its last matching

[obakamai]

object AXTests extends Specification {

  def is: SpecStructure = s2"""
          test assertions      $e1
  """
 
  def e1: MatchResult[Any] = {
    val t = 1
    val r = 3
    t must beEqualTo(4) //ignores the MatchFailure
    r must beEqualTo(3)
  }
}

This will pass as it seems the matcher will ignore the first match failure (the equals to 4) and will pass the test cause the last one match. What Am I missing here ?

[etorreborre]

Hi @obakamai. You're correct! By default, specs2 is a functional library. At its core no exceptions are thrown.
When you write t must beEqualTo(4) you get back a Result which is just a normal value.
This was done on purpose in order to:

• incite people to get into a functional mindset
• allow an easier reuse of the core library because composing code with exceptions can be difficult

This means that the default way to check 2 expectations in a default specification is to write:

(t must beEqualTo(4)) and 
(r must beEqualTo(3))

You can also reuse the fact that Result are values with a Monoid instance, so you can "sum" them by putting them in a list:

import org.specs2.fp.syntax.*

List(
  1 must beEqualTo(1),
  2 must beEqualTo(4),
  3 must beEqualTo(3),
).sumAll

This will return:

[info]  x e2
[error]  2 != 4

You might say that it is wasteful because this will evaluate all the assertions. But this can be an advantage too! Because, with a different Monoid instance for Result you can collect all the failures at once with the right imports:

import org.specs2.fp.*
import org.specs2.fp.syntax.*
import org.specs2.execute.*

given Monoid[Result] = Result.ResultFailuresMonoid(separator = "\n")

List(
  1 must beEqualTo(2),
  2 must beEqualTo(2),
  3 must beEqualTo(4),
).sumAll

This will print:

[error]  1 != 2
[error]  3 != 4

You can also go back to a more traditional style of writing assertions, with a short-circuiting behaviour.

In order to do this, extend your specification with the org.specs2.matcher.ThrownExpectations trait. Now an exception will be thrown when you write 1 must beEqualTo(4).

[obakamai]

Hi @etorreborre thanks for you reply,
Can you write your examples in Scala please (2.12; specs2 4.16.1) ? it seems there is a different implementation
Thanks!

[tabdulradi]

That's Scala 3 syntax. To make it Scala 2 replace * with _ and given Monoid[Result] with implicit val resultMonoidInstance: Monoid[Result]