title: A simple Scala Given/When/Then style specification failed
body: <p>I am new to Spec2, and trying to learn it. I come up with the following codes,</p>
  
  <pre><code>@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) =&gt; (s: String) =&gt; (n1, s.toInt)
     val result: Then[(Int, Int)] = (n: (Int, Int)) =&gt; (s: String) =&gt; ((n._1 + n._2) must_== s.toInt)
  }
  </code></pre>
  
  <p>After run it, I got <strong>java.lang.Exception: Could not instantiate class com.me.scala.start.GWTStyleSpec: null</strong> and with lots of exception stack trace below it. </p>
  
  <p>What did I do wrong for this? </p>