Property check should fail in Scalatest - scala

Question

I've created and am also using some external Scalacheck generators from Lists and appropriate types, using Gen.oneOf(List[T]) . I think it would be occasionally useful to return a placeholder for an empty value. Currently the lists are populated. How should I go about this? Do I try to append an empty type to the end of the list? If so how do I go about that? If not, how else can I get my generators to add an empty value. It seems straightforward, but I am having trouble figuring it out right now.
import org.scalatest.FlatSpec
import org.scalacheck.Gen
import org.scalacheck.Prop.exists
import org.scalatest.prop.PropertyChecks
class EventFieldGeneratorTest extends FlatSpec with PropertyChecks {
behavior of "Gen.option"
it should "occasionally return None" in {
val colors = Gen.oneOf("Blue", "Red", "Green", "Yellow")
val opt = Gen.option(colors)
val list = Gen.listOfN(20, opt)
val p1 = exists(list)(_ == None)
p1.check
}
}
Can anybody explain why my test is giving up?
Testing started at 10:31 AM ... ! Gave up after only 0 passed tests. 501 tests were discarded.
Process finished with exit code 0
How can I mark that as a failed result for ScalaTest? Is it a bad idea for me to use Flatspec?
Maybe I should be using something other than check...
Here's the documentation I used to sort it on. On the Scalatest page:
http://www.scalatest.org/user_guide/writing_scalacheck_style_properties

Answer 1

I don't think there's anything flawed with trying to use lists with optional values. There are just a few issues you're running in to that are giving you trouble.
It's confusing, but if you're using the Scalatest framework, you need to use the Scalatest infrastructure to use Scalacheck. So you'll need to use Scalatest matchers, and write Scalatest-flavored properties (using it's forAll), but you'll still use Scalacheck's generators directly.
For some reason the type inference between lists and Option type is giving you trouble. If you use the shouldBe matcher,
x shouldBe(None)
you'll get a relevant runtime error from Scalatest:
[info] - should occasionally return None *** FAILED ***
[info] TestFailedException was thrown during property evaluation.
[info] Message: List() was not equal to None
[info] Location: (GenTest.scala:13)
[info] Occurred when passed generated values (
[info] arg0 = List() // 5 shrinks
[info] )
[info] Run completed in 1 second, 621 milliseconds.
[info] Total number of tests run: 1
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 0, failed 1, canceled 0, ignored 0, pending 0
You shouldn't be matching a list with an Option type. You need to be matching with the Scalatest "container" matcher should contain
import org.scalatest.FlatSpec
import org.scalatest.Matchers
import org.scalacheck.Gen
import org.scalatest.prop.PropertyChecks
class EventFieldGeneratorTest extends FlatSpec with Matchers with PropertyChecks {
behavior of "Gen.option"
it should "occasionally return None" in {
val colors = Gen.oneOf("Blue","Red","Green","Yellow")
val opt = Gen.option(colors)
val list = Gen.listOfN(20,opt)
forAll(list) { (xs: List[Option[String]]) =>
xs should contain (None)
}
}
}
This gives you a successful property check:
[info] EventFieldGeneratorTest:
[info] Gen.option
[info] - should occasionally return None
[info] ScalaTest
[info] Run completed in 1 second, 9 milliseconds.
[info] Total number of tests run: 1
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 1, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.
[info] Passed: Total 1, Failed 0, Errors 0, Passed 1
More on Scalatest matchers
http://www.scalatest.org/user_guide/using_matchers