Some List specs2 matcher

Question

Why doesn't the following work?

Some(List()) must beSome(Nil)

'Some(List())' is Some but List() is not equal to 'org.specs2.matcher.ValueChecks$$anon$3@480ba116'

Answer 1

Note that

Some(List()) must beSome(List())

also don't work.

 'Some(List())' is Some but List() is not equal to 
 'org.specs2.matcher.ValueChecks$$anon$4@48d1978f' 
 Actual:   List()
 Expected: org.specs2.matcher.ValueChecks$$anon$4@48d1978f

So the problem is not Nil

We know that what we are really doing is something like:

 Some(List()).must(beSome(List()))

The problem seems with beSome. Let's see what beSome is returning:

val bl = beSome(List())  // SomeCheckedMatcher[Int]
val bn = beSome(Nil)     // SomeCheckedMatcher[Int]

This doesn't seen right since the return type is like were are checking an Option for a Integer:

val b = beSome(2)        // SomeCheckedMatcher[Int]

And those are not our target types:

val myList = List()  // myList: List[Nothing] = List()
val myList2 = Nil    // myList2: scala.collection.immutable.Nil.type = List()

So, what's wrong?

Looking at the documentation (Option/Either), you can use beSome the folowing ways:

• beSome check if an element is Some(_)

• beSome(exp) check if an element is Some(exp)

• beSome(matcher) check if an element is Some(a) where a satisfies the matcher

• beSome(function: A => AsResult[B]) check if an element is Some(a) where function(a) returns a successful Result (note that a Seq[A] is also a function Int => A so if you want to check that a sequence is contained in Some you need to use a matcher: beSome(===(Seq(1)))

The last alternative seems to be our problem here. Note the List() is like Seq, a function from Int => A. In, our example:

val myList = List()                 // myList: List[Nothing] = List()
val func: Int => Nothing = myList   // func: Int => Nothing = List()

To fix this we should use a matcher (the third alternative of the documentation):

Some(List()) must beSome(beEqualTo(List()))
Some(List()) must beSome(beEqualTo(Nil))

// or 

Some(List()) must beSome(be_==(List()))  
Some(List()) must beSome(be_==(Nil))