A simple Scala Given/When/Then style specification

Question

I am new to Spec2, and trying to learn it. I come up with the following codes,

@RunWith(classOf[JUnitRunner])
class GWTStyleSpec extends Specification {
    "A given-when-then example for the addition" ^
       "Given the following number: ${1}" ^ number1 ^
       "And a second number: ${2}" ^ number2 ^
       "Then I should get: ${3}" ^ result ^
     end
   val number1: Given[Int] = (_: String).toInt
   val number2: When[Int, (Int, Int)] = (n1: Int) => (s: String) => (n1, s.toInt)
   val result: Then[(Int, Int)] = (n: (Int, Int)) => (s: String) => ((n._1 + n._2) must_== s.toInt)
}

After run it, I got java.lang.Exception: Could not instantiate class com.me.scala.start.GWTStyleSpec: null and with lots of exception stack trace below it.

What did I do wrong for this?

Answer 1

If you are importing org.specs2.Specification then there should be a def is = ... method defined:

@RunWith(classOf[JUnitRunner])
class GWTStyleSpec extends Specification { def is = 
  "A given-when-then example for the addition" ^
     "Given the following number: ${1}"        ^ number1 ^
     "And a second number: ${2}"               ^ number2 ^
     "Then I should get: ${3}"                 ^ result ^
                                               end
  lazy val number1: Given[Int] = (_: String).toInt
  lazy val number2: When[Int, (Int, Int)] = (n1: Int) => (s: String) => (n1, s.toInt)
  lazy val result: Then[(Int, Int)] = (n: (Int, Int)) => (s: String) => ((n._1 + n._2) must_== s.toInt)
}

It is also possible that the vals are not being instantiated properly so you can try using lazy vals.

Note also that the next specs2 version (1.15-SNAPSHOT) proposes another style of Given/When/Then specifications based on Scala 2.10 features:

class GivenWhenThenInterpolatedSpec extends Specification with GivenWhenThen { def is = sequential ^ s2"""                   

 A given-when-then example for a calculator                                                                                  
   Given the following number: 1                             $aNumber                                                        
   And a second number: 2                                    $aNumber                                                        
   And a third number: 6                                     $aNumber                                                        
   When I use this operator: +                               $operator                                                       
   Then I should get: 9                                      $result                                                         
   And it should be >: 0                                     $greaterThan                                                    

 Now with the multiplication                                                                                                 
   Given the following number: 4                             $aNumber                                                        
   And a second number: 5                                    $aNumber                                                        
   And a third number: 6                                     $aNumber                                                        
   When I use this operator: *                               $operator                                                       
   Then I should get: 120                                    $result                                                         
   And it should be >: 10                                    $greaterThan                                                    
   But not should be >: 150                                  $lowerThan                                                      
                                                             """                                                             

  val readInt = groupAs("\\d+")                                                                                              
  val readOperator = readAs(".*: (.)$")                                                                                      
  val aNumber: Given[Int] = readInt and { s: String => s.toInt }                                                             

  // when there are too many Given[T, S] consecutive steps, it is possible to follow them with a When[Seq[T], S]             
  val operator: When[Seq[Int], Operation] = readOperator and { (numbers: Seq[Int]) => (s: String) => Operation(numbers, s) } 

  val result: Then[Operation] = readInt andThen { (operation: Operation) => (s: String) =>                                   
    operation.calculate  must_== s.toInt                                                                                     
  }                                                                                                                          
  val greaterThan: Then[Operation] = readInt andThen { (operation: Operation) => (s: String) =>                              
    operation.calculate  must be_>= (s.toInt)                                                                                
  }                                                                                                                          
  val lowerThan: Then[Operation] = readInt andThen { (operation: Operation) => (s: String) =>                                
    operation.calculate  must be_<= (s.toInt)                                                                                
  }                                                                                                                          

  case class Operation(numbers: Seq[Int], operator: String) {                                                                
    def calculate: Int = if (operator == "+") numbers.sum else numbers.product                                               
  }                                                                                                                          

}