FsCheck DataGen为空

Question

我正在尝试通过一个FsCheck的例子来研究一种带有歧视工会的类型，以便为我们更大的项目建立最佳实践。现在，我从我的生成器得到零，我不知道为什么。在下面的代码中，DataGen.containerGenerator为null。

namespace Container
open System
open Xunit
open FsCheck

module ContainerLibrary = 
    type [<Measure>] oz

    type Container = 
        | Cup of Common
        | Bowl of Common
    and Common = 
        { Volume    :decimal<oz>
          Weight    :decimal}

module DataGen = 
    type Generators = 
        static member arbVolume = 
            FsCheck.Gen.choose (1, 16)
            |> FsCheck.Gen.map(fun x -> (decimal x / 8.0M) * 1.0M<ContainerLibrary.oz>)
            |> FsCheck.Arb.fromGen

    FsCheck.Arb.register<Generators>() |> ignore

    let bowlGenerator = 
        FsCheck.Gen.map2 (fun a b -> ContainerLibrary.Bowl( { Volume = a 
                                                              Weight = b})) 
                         (Generators.arbVolume.Generator) 
                         (FsCheck.Arb.generate<decimal>)
    let cupGenerator =
        FsCheck.Gen.map2 (fun a b -> ContainerLibrary.Cup( { Volume = a 
                                                             Weight = b})) 
                         (Generators.arbVolume.Generator) 
                         (FsCheck.Arb.generate<decimal>)

    let containerGenerator =
        Gen.oneof [bowlGenerator; cupGenerator]

module Tests =
    [<Fact;>]
    let ``01 : Containers must be no more than 20 oz`` () =
        //Is this the best way to get one of something?
        let c = FsCheck.Gen.sample 0 1 DataGen.containerGenerator |> Seq.head
        Assert.NotNull (c)

Answer 1

当我运行它时，它看起来并不是空的，即使我得到了更多的值。您使用的是哪个版本的FsCheck？

[<Fact;>]
let ``01 : Containers must be no more than 20 oz`` () =
    //Is this the best way to get one of something?
    Gen.sample 0 100 DataGen.containerGenerator |> Seq.iter(fun c -> printf "%A" c; Assert.NotNull (c))

在任何情况下，对于你正在做的事情，有几件事情需要注意。

• FsCheck使用反射来注册生成器；反射不能看到度量类型参数的类型。因此，对于所有小数，Arb.register实际上都会覆盖十进制生成器。
• 不知怎么的FsCheck。你所使用的资格令人困惑，智力感无止境。
• Gen.sample是测试生成器的一种合理方法，但我主要是在交互式设置中使用它；如果您经历了设置测试的麻烦，我倾向于使用FsCheck内置的测试用例观察功能。参见此处的“观察测试用例分布”：https://fsharp.github.io/FsCheck/Properties.html
• 在模块init中使用Arb.register有点易碎，这取决于F#中的模块初始化规则来注册生成器。如果您正在使用Xunit，最好使用内置集成来减少这方面不可避免的挫折。

考虑到以下几点，我重写了您的示例：

module DataGen = 

open ContainerLibrary

//can't really register this one because of the measure, would override all decimal generatos
let volumeGenerator = 
        Gen.choose (1, 16)
        |> Gen.map(fun x -> (decimal x / 8.0M) * 1.0M<ContainerLibrary.oz>)

let commonGenerator =
    Gen.map2 (fun a b -> { Volume = a 
                           Weight = b})
                     (volumeGenerator) 
                     (Arb.generate<decimal>)

//in case you like applicative style, otherwise completely equivalent
let commonGeneratorAlternative =
    (fun a b -> { Volume = a; Weight = b}) <!> volumeGenerator <*> Arb.generate<decimal>

let bowlGenerator = Gen.map Bowl commonGenerator
let cupGenerator = Gen.map Cup commonGenerator

let containerGenerator =
    Gen.oneof [bowlGenerator; cupGenerator]

type Generators =
    static member Container() = containerGenerator |> Arb.fromGen

module Tests =
open FsCheck.Xunit
open ContainerLibrary

//use PropertyAttribute from FsCheck.Xunit
//use the defined container generator - can also move this to module level
//other ways to parametrize
[<Property(Arbitrary=[|typeof<DataGen.Generators>|])>]
//thanks to PropertyAttribute can now just take container as argument
let ``01 : Containers must be no more than 20 oz`` (container:Container) =
    match container with
    | Cup common
    | Bowl common -> common.Volume <= 20.0M<oz>
    |> Prop.collect container //see the generated values in the output

它输出的输出类似于：

好的，通过了100次测试。

1%杯{体积= 2.0M；重量=-0.00002213609288587415609M；}1%杯{体积= 1.8750M；重量= 922337.20325598085121M;}等