Question

我到处都有一堆带有字符串的类型。我想使用FsCheck编写针对在这些类型上运行的函数的属性测试。对于所有这些，我知道我永远不会得到为null或非字母数字的字符串。因此，我想相应地限制字符串的值生成。

我尝试过：

let charSet= "abc" // simplified for the example
let isValidString (s:string) = null<>s && not (s |> Seq.exists (fun c -> not (charSet |> Seq.contains c)))
let createConfig left right = {LeftLanguageName= left; RightLanguageName= right}
let generateString= Arb.generate<string> |> Gen.filter isValidString
let generateConfig= createConfig <!> generateString <*> generateString 

type Generators =
  static member String() =
    { 
        new Arbitrary<string>() with
            override x.Generator = generateString
    }
  static member LanguageConfiguration()= 
    {
        new Arbitrary<LanguageConfiguration>() with
           override x.Generator = generateConfig
    }

Arb.register<Generators>() |> ignore

但是，FsCheck会不断生成这样的值

Falsifiable, after 14 tests (9 shrinks) (StdGen (2144073619,296598634)):
Original:
{LeftLanguageName = " 1c\J
";
 RightLanguageName = "\026z^k";} (At least one control character has been escaped as a char code, e.g. \023)
Shrunk:
{LeftLanguageName = "
";
 RightLanguageName = "";}

所以很明显我缺少了一些东西，但是我不知道是什么。

我看着

How to generate null strings for FsCheck tests

和

http://blog.nikosbaxevanis.com/2015/09/25/regex-constrained-strings-with-fscheck/

，但是它们都没有尝试在全局范围内（在范围内）覆盖字符串生成。

Answer 1

我无法重现该问题。使用FSCheck 2.14.0，我尝试在F＃脚本文件中运行以下命令：

#r "C:/Temp/nuget/packages/fscheck/lib/net452/FsCheck.dll"
open FsCheck

type LanguageConfiguration = 
  { LeftLanguageName:string; RightLanguageName:string }

let charSet= "abc" // simplified for the example
let isValidString (s:string) = 
  null<>s && not (s |> Seq.exists (fun c -> not (charSet |> Seq.contains c)))
let createConfig left right = {LeftLanguageName= left; RightLanguageName= right}
let generateString= Arb.generate<string> |> Gen.filter isValidString
let generateConfig= createConfig <!> generateString <*> generateString 

type Generators =
  static member String() =
    { new Arbitrary<string>() with
            override x.Generator = generateString }
  static member LanguageConfiguration()= 
    { new Arbitrary<LanguageConfiguration>() with
           override x.Generator = generateConfig }

Arb.register<Generators>() |> ignore

Check.QuickThrowOnFailure (fun (n:LanguageConfiguration) ->
  printfn "%A" n
  true)

这将运行100个测试，并且输出如下所示：

{LeftLanguageName = "";
 RightLanguageName = "";}
{LeftLanguageName = "";
 RightLanguageName = "";}
{LeftLanguageName = "";
 RightLanguageName = "";}
{LeftLanguageName = "";
 RightLanguageName = "";}
{LeftLanguageName = "";
 RightLanguageName = "";}

这表明您的测试生成还有另一个问题（也许只是在这个简化的演示中），这是因为您的Gen.filter isValidString调用基本上消除了所有有趣的输入，因为它们是无效的。

您可以通过不同方式生成字符串来解决此问题-更好的方法是生成一个int值作为长度，然后在循环中从允许的字符集中生成一个字符，然后进行串联这些字符（只为您提供有效字符串）。

如何覆盖FsCheck中所有属性的字符串生成

1 个答案: