Return type from specs2 helper method

Question

Let's assume I write a helper method, that accepts some test code.

def testWithPrintln(test: => A):A = {
    println("I'm happy and testing")
    test
}

What should be the A type be? What is the right one? I'm browsing the specs2 api and there are numerous similar looking types: AsResult[_], Result, MatchResult[_], I'm confused what to use.

Answer 1

Trying to elaborate on @cmbaxter's answer.

In specs2 the body of an Example needs to be evaluated as a Result, that is either a Success or Failure or Error or Skipped or Pending. In order to provide enough flexibility, the body of an Example will accept any type T that can be transformed to a Result provided that an instance of AsResult[T] is in (the implicit) scope.

There are instances of AsResult for various types:

• Boolean: this makes true being a Success and false being a failure

• Result itself, just returning the value

• MatchResult[T]: a MatchResult is the result of a matcher execution. This is the result of expressions such as 1 must beEqualTo(1)

• org.scalacheck.Prop to execute a ScalaCheck property in an example

In your example, the test helper will work fine if you implement it like this:

// if `a: A` is acceptable as the body of an example
// you can use testWithPrintln(a) in your example
def testWithPrintln[A : AsResult](a: A): A = {
  println(a)
  a
} 

Note however that the helper you are looking for might already exist in specs2. You can use the .pp method to "print and pass" any value:

// has type MatchResult[Int]
(1 must_== 1).pp

Also you can add more verbose messages to your expectations:

 // will print "this is not correct because 1 is not equal to 2"
 "this is correct" ==> { 1 must_== 2 }

 // will print "the number of elements: 1 is not greater than 2
 val n = 1
 n aka "the number of elements" must be_>(2)