scalacheck

We are looking for a viable design pattern for building Scalacheck Gen (generators) that can produce both positive and negative test scenarios. This will allow us to run forAll tests to validate functionality (positive cases), and also verify that our case class validation works correctly by failing on all invalid combinations of data. Making a simple, parameterized Gen that does this on a one-off basis is pretty easy. For example: def idGen(valid: Boolean = true): Gen[String] = Gen.oneOf(ID.values.toList).map(s => if (valid) s else Gen.oneOf(simpleRandomCode(4), "").sample.get) With the above

I've wrote the following spec "An IP4 address" should "belong to just one class" in { val addrs = for { a <- Gen.choose(0, 255) b <- Gen.choose(0, 255) c <- Gen.choose(0, 255) d <- Gen.choose(0, 255) } yield s"$a.$b.$c.$d" forAll (addrs) { ip4s => var c: Int = 0 if (IP4_ClassA.unapply(ip4s).isDefined) c = c + 1 if (IP4_ClassB.unapply(ip4s).isDefined) c = c + 1 if (IP4_ClassC.unapply(ip4s).isDefined) c = c + 1 if (IP4_ClassD.unapply(ip4s).isDefined) c = c + 1 if (IP4_ClassE.unapply(ip4s).isDefined) c = c + 1 c should be (1) } } That is very clear in its scope. The test passes successfully but

I would like to make my ScalaCheck property tests in my specs2 test suite deterministic, temporarily, to ease debugging. Right now, different values could be generated each time I re-run the test suite, which makes debugging frustrating, because you don't know if a change in observed behaviour is caused by your code changes, or just by different data being generated. How can I do this? Is there an official way to set the random seed used by ScalaCheck? I'm using sbt to run the test suite. Bonus question: Is there an official way to print out the random seed used by ScalaCheck, so that you can

I'm trying to generate random data with Scalacheck. I have a hierarchy of case classes with many properties. The only way I've found so far to populate the case classes is like this : case class Data(a: String, b: String, c: String) val genLigneDecompte: Gen[Data] = for { ag <- Gen.alphaStr bg <- Gen.alphaStr cg <- Gen.alphaStr } yield Data( a = ag, b = bg, c = cg ) For a case class with 10-20 properties it's pretty tedious. I was wondering if there was a way to automate it somehow... I am sure somebody will come up with a solution that abstracts over arity using shapeless . But there are some

I wonder why Arbitrary is needed because automated property testing requires property definition, like val prop = forAll(v: T => check that property holds for v) and value v generator. The user guide says that you can create custom generators for custom types (a generator for trees is exemplified). Yet, it does not explain why do you need arbitraries on top of that. Here is a piece of manual implicit lazy val arbBool: Arbitrary[Boolean] = Arbitrary(oneOf(true, false)) To get support for your own type T you need to define an implicit def or val of type Arbitrary[T]. Use the factory method