关于 scala:ScalaCheck: Gen.choose 输出超出指定范围的值

ScalaCheck: Gen.choose outputting values beyond a specified range

我正在使用 Scalacheck 来查找缺陷，作为作业的一部分。也许令人难以置信的是，我被卡住了，因为它正在生成一对非零整数。

来自我的 IntelliJ 工作表，逐字逐句：

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import org.scalacheck._
import Arbitrary._
import Gen._
import Prop._

implicit lazy val genUnequalIntPairs = for {
i <– Gen.choose(1,1000)
j <– Gen.choose(i+1,1000)
if (i < j)
} yield (i,j)

val kk = forAll (genUnequalIntPairs) {
case (x,y) => println(“x =” + x +“, y =” + y)
x == y
}

kk.check

因为，我明确提到所选值的最小值为非零，所以我不应该在属性内看到任何零，对吧？至少，这是我的理解。但这就是我所看到的：

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x =134, y =547
x =0, y =547
x =0, y =0
x =0, y =274
x =0, y =0
x =0, y =137
x =0, y =0
x =0, y =69
x =0, y =0
x =0, y =35
x =0, y =0
x =0, y =18
x =0, y =0
x =0, y =9
x =0, y =0
x =0, y =5
x =0, y =0
x =0, y =3
x =0, y =0
x =0, y =2
x =0, y =0
x =0, y =1
x =0, y =0
! Falsified after 0 passed tests.
> ARG_0: (0,1)
> ARG_0_ORIGINAL: (134,547)
res0: Unit = ()

这些零是从哪里来的？我错过了什么？也许，一些显而易见的东西，但我的眼睛没有捕捉到它们。

我使用的是 Scalcheck 1.12.1 版

1	Seq(“org.scalacheck” %%“scalacheck” %“1.12.1”)

任何帮助，不胜感激。

更新 I：正如@samar 所建议的(我还在 gitbook 中找到了相同的参考)，我尝试使用这样的过滤器过滤生成器。但运气不佳(代码如下)：

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implicit lazy val genUnequalIntPairs = for {
i <– Gen.choose(1,1000).suchThat(_ > 0)
j <– Gen.choose(i+1,1000).suchThat(_ > 0)
if (i < j)
} yield (i,j)

val kk = forAll (genUnequalIntPairs) {
case (x,y) => println(“x =” + x +“, y =” + y)
x == y
}

kk.check

我运行了这段代码大约 6-7 次。这是一个随机输出。

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x =536, y =730
x =0, y =730
x =0, y =0
x =0, y =365
x =0, y =0
x =0, y =183
x =0, y =0
x =0, y =92
x =0, y =0
x =0, y =46
x =0, y =0
x =0, y =23
x =0, y =0
x =0, y =12
x =0, y =0
x =0, y =6
x =0, y =0
x =0, y =3
x =0, y =0
x =0, y =2
x =0, y =0
x =0, y =1
x =0, y =0
! Falsified after 0 passed tests.
> ARG_0: (0,1)
> ARG_0_ORIGINAL: (536,730)
res0: Unit = ()

更新二：为了确认，我已经按照 Eric 的建议做了这个：

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implicit lazy val genUnequalIntPairs = for {
i <– Gen.choose(1,1000)
j <– Gen.choose(i+1,1000)
if (i != 0 && j != 0)
} yield {
(i,j)
}

val kk = forAllNoShrink(genUnequalIntPairs) {
case (x,y) => println(“x =” + x +“, y =” + y)
x < y
}

kk.check

这行得通：

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x =805, y =1000
x =742, y =926
x =772, y =919
x =219, y =686
x =999, y =1000
x =752, y =792
x =163, y =585
x =721, y =735
x =251, y =866
x =383, y =887
x =797, y =939
x =925, y =947
x =291, y =951
x =502, y =619
x =422, y =756
x =159, y =886
x =49, y =955
x =624, y =819
x =922, y =979
x =881, y =894
x =936, y =952
x =908, y =975
x =802, y =976
x =918, y =946
x =564, y =823
x =544, y =751
x =916, y =938
x =57, y =762
x =614, y =963
x =497, y =986
x =102, y =332
x =264, y =643
x =611, y =720
x =542, y =797
x =704, y =784
Output exceeds cutoff limit.

更新三：
FWIW，我发现通过迁移到 Scalacheck 版本 1.13.1(最初是 1.12.x)，我得到以下行为：

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implicit lazy val genUnequalIntPairs = for {
i <– Gen.choose(1,1000)
j <– Gen.choose(1,1000)
if (i < j)
} yield {
(i,j)
}

val kk = forAll(genUnequalIntPairs) {
case (x,y) => println(“x =” + x +“, y =” + y)
x < y
}

kk.check

产生

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x =56, y =752
x =395, y =532
x =468, y =828
x =326, y =749
x =203, y =973
x =294, y =393
x =589, y =975
x =44, y =75
x =406, y =533
x =33, y =381
x =405, y =767
x =13, y =883
x =201, y =341
x =593, y =991
x =636, y =913
x =508, y =782
x =333, y =861
x =306, y =863
x =428, y =537
x =373, y =775
x =74, y =462
x =196, y =299
x =245, y =535
x =312, y =993
x =940, y =989
x =12, y =708

但是通过将条件从小于更改为相等，会发生这种情况：

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implicit lazy val genUnequalIntPairs = for {
i <– Gen.choose(1,1000)
j <– Gen.choose(1,1000)
if (i < j)
} yield {
(i,j)
}

val kk = forAll(genUnequalIntPairs) {
case (x,y) => println(“x =” + x +“, y =” + y)
x == y
}

kk.check

产生

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x =370, y =585
x =0, y =585
x =0, y =0
x =0, y =293
x =0, y =0
x =0, y =147
x =0, y =0
x =0, y =74
x =0, y =0
x =0, y =37
x =0, y =0
x =0, y =19
x =0, y =0
x =0, y =10
x =0, y =0
x =0, y =5
x =0, y =0
x =0, y =3

显然，所应用的条件会覆盖我在生成器中留下的显式指令。这不是有点不直观吗？别人怎么看？