如何为FsCheck测试生成空字符串 [英] How to generate null strings for FsCheck tests

问题描述

使用Haskell QuickCheck测试库的F＃版本 FsCheck 从C# ，我发现随机字符串生成器不会生成空字符串。

Using FsCheck, the F# version of the Haskell QuickCheck test library, to generate tests from C#, I found that the random string generator does not generate the null string.

using FsCheck.Fluent;
Spec.ForAny<string>(s => s != null).QuickCheck(); // always pass

此外，似乎没有设计处理空字符串的方法，但我没有做到从文档中将其固定下来。例如，仅在两个字符串（其中之一为null）之间进行选择将不起作用：

Furthermore, there seems not to handle null strings by design, but I have not managed to pin it down from the documentation. For example, just picking between two strings, one of them null, won't work:

var strings = Any.ValueIn<string>(null, "non-null string");
Spec.For(strings, s => true).QuickCheck(); // throws null ref exception

字符串似乎是一种特殊情况，因为它可以处理定制的

And strings seem to be a special case, because it handles custom-made objects such as

class Thing {}

当与空值混合时：

var objects = Any.ValueIn(null, new Thing());
Spec.For(objects, s => true).QuickCheck(); // pass

推荐答案

我试图对此进行深入研究并且似乎您在FsCheck中发现了一个错误。

I tried to dig a bit into this and it appears that you have discovered a bug in FsCheck.

问题似乎出在文件Arbitrary.fs中，并且实际上仅与字符串有关。我必须替换掉它，他们在字符串上调用ToCharArray

It appears that the problem is in file Arbitrary.fs and is really only string-related. I had to replace this, where they call ToCharArray on the string

    static member String() = 
        { new Arbitrary<string>() with
            override x.Generator = Gen.map (fun chars -> new String(List.toArray chars)) generate
            override x.Shrinker s = s.ToCharArray() |> Array.toList |> shrink |> Seq.map (fun chars -> new String(List.toArray chars))
        }

具有此

    static member String() = 
        { new Arbitrary<string>() with
            override x.Generator = Gen.map (fun chars -> new String(List.toArray chars)) generate
            override x.Shrinker s = 
                match s with
                    | null  -> seq {yield null;}
                    | _ -> s.ToCharArray() |> Array.toList |> shrink |> Seq.map (fun chars -> new String(List.toArray chars))
        }

您可能想与fscheck开发人员在此处进行讨论，同时还要检查我的修复程序是否运作良好-也许有更好的方法来实现它，但是对于已经知道代码的人来说，它会更简单。

You may want to raise this with fscheck developers here and also check if my fix works well - there is probably a better way to implement it, but it would be simpler for someone, who already knows the code.

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