使用 FsCheck 属性时如何排除空值? [英] How to exclude null value when using FsCheck Property attribute?

问题描述

我需要编写一个简单的方法来接收一个参数(例如一个 string)并执行 smth.通常我最终会进行两次测试.第一个是保护条款.第二个将验证预期行为(为简单起见，该方法不应失败):

I need to write a simple method that receives a parameter (e.g. a string) and does smth. Usually I'd end up with two tests. The first one would be a guard clause. The second would validate the expected behavior (for simplicity, the method shouldn't fail):

[Fact]
public void DoSmth_WithNull_Throws()
{
    var sut = new Sut();
    Assert.Throws<ArgumentNullException>(() =>
        sut.DoSmth(null));
}

[Fact]
public void DoSmth_WithValidString_DoesNotThrow()
{
    var s = "123";
    var sut = new Sut();
    sut.DoSmth(s); // does not throw
}

public class Sut
{
    public void DoSmth(string s)
    {
        if (s == null)
            throw new ArgumentNullException();

        // do smth important here
    }
}

当我尝试使用 FsCheck [Property] 属性来生成随机数据，null 和许多其他随机值被传递给测试，这在某些时候会导致 NRE:

When I try to utilize the FsCheck [Property] attribute to generate random data, null and numerous other random values are passed to the test which at some point causes NRE:

[Property]
public void DoSmth_WithValidString_DoesNotThrow(string s)
{
    var sut = new Sut();
    sut.DoSmth(s); // throws ArgumentNullException after 'x' tests
}

我意识到这就是 FsCheck 生成大量随机数据以涵盖不同情况的全部想法，这绝对是很棒的.

I realize that this is the entire idea of FsCheck to generate numerous random data to cover different cases which is definitely great.

是否有任何优雅的方法来配置 [Property] 属性以排除不需要的值?(在这个特定的测试中，null).

Is there any elegant way to configure the [Property] attribute to exclude undesired values? (In this particular test that's null).

推荐答案

FsCheck 有一些内置类型，可用于指示特定行为，例如，引用类型值不应为 null.其中之一是NonNull<'a>.如果您要求其中之一，而不是要求原始字符串，您将不会得到空值.

FsCheck has some built-in types that can be used to signal specific behaviour, like, for example, that reference type values shouldn't be null. One of these is NonNull<'a>. If you ask for one of these, instead of asking for a raw string, you'll get no nulls.

在 F# 中，您可以将其分解为函数参数:

In F#, you'd be able to destructure it as a function argument:

[<Property>]
let DoSmth_WithValidString_DoesNotThrow (NonNull s) = // s is already a string here...
    let sut = Sut ()
    sut.DoSmth s // Use your favourite assertion library here...
}

我认为在 C# 中，它应该看起来像这样，但我还没有尝试过:

I think that in C#, it ought to look something like this, but I haven't tried:

[Property]
public void DoSmth_WithValidString_DoesNotThrow(NonNull<string> s)
{
    var sut = new Sut();
    sut.DoSmth(s.Get); // throws ArgumentNullException after 'x' tests
}

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