在FsCheck中，如何生成带有非负字段的测试记录?

问题描述

在F#中，我有一条记录，其中包含一些字段:

In F#, I have a record with a few fields:

    type myRecord = { a:float; b:float; c:float }

我正在使用FsCheck来测试使用此记录的某些属性.对于(人为的)示例，

I am using FsCheck to test some properties which use this record.For (a contrived) example,

    let verify_this_property (r:myRecord) = myFunction(r) = (r.a * r.b) / r.c

由于 myFunction 的内部实现限制，我希望FsCheck创建测试用例，其中每个字段a，b，c都限于非负浮点数.

Due to the internal implementation restrictions of myFunction, I would like to have FsCheck create test cases in which each of the fields a,b,c are restricted to non-negative floats.

我怀疑这需要为 myRecord 创建一个生成器，但是我找不到任何执行此操作的示例.

I suspect this requires creating a generator for myRecord, but I have not been able to find any examples of how to do this.

任何人都可以提供指导吗?

Can anyone supply guidance?

推荐答案

尝试一下:

type Generators = 
    static member arbMyRecord =
        fun (a,b,c) -> { myRecord.a = a; b = b; c = c }
        <!> (Arb.generate<float> |> Gen.suchThat ((<) 0.) |> Gen.three)
        |> Arb.fromGen

Arb.register<Generators>() |> ignore
Check.Quick verify_this_property

<!>是一个后缀map，对于应用样式很有用.这是一个等效的生成器:

The <!> is an infix map, useful for applicative style. This is an equivalent generator:

type Generators = 
    static member arbMyRecord =
        Arb.generate<float> 
        |> Gen.suchThat ((<) 0.) 
        |> Gen.three
        |> Gen.map (fun (a,b,c) -> { myRecord.a = a; b = b; c = c })
        |> Arb.fromGen

如果您不想全局注册生成器，则可以使用forAll:

If you don't want to globally register your generator, you can use forAll:

Check.Quick (forAll Generators.arbMyRecord verify_this_property)

向左收缩是一种锻炼；)

Shrinking left as an exercise ;)

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