scala - Gen.sequence 忽略给定 Traversable 的大小

Question

Gen.sequence 似乎忽略了给定Traversable 的大小。这是设计使然吗？我正在使用版本 1.14.0 和 Scala 2.13。跟随生成器

Gen.sequence[List[Int], Int](List.fill(3)(Gen.const(5)))

有时会生成大小为 1 的列表。我缺少什么？

示例测试

import org.scalacheck.Gen
import org.scalatest.concurrent.ScalaFutures
import org.scalatest.{Assertions, FlatSpec, Inside, Inspectors, Matchers, OptionValues}
import org.scalatestplus.scalacheck.ScalaCheckPropertyChecks

class RuleSpec extends FlatSpec with Matchers with Assertions with OptionValues with Inside with Inspectors with ScalaFutures with ScalaCheckPropertyChecks {

  val filterGen = Gen.listOfN(3, Gen.const(5))
  val inputGen = Gen.pick(10, 5 to 15).map(_.toList).filter(_.nonEmpty)

  "A HasAny rule with partially matching filter" should "validate input" in {
    forAll(filterGen, inputGen) { case (filter, input) =>
      val result = HasAny(filter: _*).valid(input)
      println(s"$result: $filter   ${input}\n")
      result should be(true)
    }
  }
}

Answer 1

这可能是由于 Test Case Minimisation

One interesting feature of ScalaCheck is that if it finds an argument that falsifies a property, it tries to minimise that argument before it is reported. This is done automatically when you use the Prop.property and Prop.forAll methods to create properties, but not if you use Prop.forAllNoShrink.

因此尝试像这样使用 Prop.forAllNoShrink

Prop.forAllNoShrink(filterGen, inputGen) { case (filter, input) => ...

如果使用 ScalaTest 的 forAll，请尝试 Add support for not shrinking values in GeneratorDrivenPropertyChecks #584 中的建议通过创建以下特征

trait NoShrink {
  implicit def noShrink[A]: Shrink[A] = Shrink(_ => Stream.empty)
}

并将其混合在规范中，如下所示

class RuleSpec extends FlatSpec ... with ScalaCheckPropertyChecks with NoShrink {
  ...
    forAll(filterGen, inputGen) { case (filter, input) => ...