Specs2 + Scalacheck Generate Tuple with different Strings

Question

I have to test an loop-free graph and always checking whether the Strings are different is not very usable (it throws an exception). There must be a better solution, but I am not able to come up with it, and i am kind of lost in the specs2 documentation. This is an example of the code:

"BiDirectionalEdge" should {
"throw an Error for the wrong DirectedEdges" in prop {
  (a :String, b :String, c :String, d :String) =>
    val edge1 = createDirectedEdge(a, b, c)
    val edge2 = createDirectedEdge(c, b, d)
    new BiDirectionalEdge(edge1, edge2) must throwA[InvalidFormatException] or(a mustEqual d)
}

if a and c are the same, createDirectedEdge will throw an exception (i have different test for that behaviour).

Answer 1

Yep, there's a better way—this is precisely what conditional properties are for. Just add your condition followed by ==>:

"BiDirectionalEdge" should {
  "throw an Error for the wrong DirectedEdges" in prop {
    (a: String, b: String, c: String, d: String) => (a != c) ==>
      val edge1 = createDirectedEdge(a, b, c)
      val edge2 = createDirectedEdge(c, b, d)
      new BiDirectionalEdge(edge1, edge2) must
        throwA[InvalidFormatException] or(a mustEqual d)
  }
}

If the condition is likely to fail often, you should probably take a different approach (see the ScalaCheck guide for details), but in your case a conditional property is totally appropriate.