如何在Rust中模拟特定的方法，但不是全部? [英] How to mock specific methods but not all of them in Rust?

问题描述

我很难确定目标结构的方法的单元测试.

I have troubles figuring out unit tests for the methods of the target struct.

我有一个方法random_number根据结构的属性返回一个随机值，还有另一个方法plus_one接受第一个方法的结果并对其进行处理:

I have a method random_number that returns a random value based on the attribute of the struct and there is another method plus_one that takes the result of the first method and does something with it:

pub struct RngTest {
    pub attr: u64,
}

impl RngTest {
    pub fn random_number(&self) -> u64 {
        let random = 42; // lets pretend it is random
        return random * self.attr;
    }

    pub fn plus_one(&self) -> u64 {
        return self.random_number() + 1;
    }
}

对第一种方法进行单元测试，对另一种方法进行测试的策略是什么?我想模拟plus_one()的单元测试的self.random_number()输出，使其在单元测试中具有健全的代码.有一篇不错的文章比较了不同的模拟库，并得出结论(足够可笑)，它们都不是与其他人脱颖而出真的很棒.

Having a unit test for the first method, what is the strategy to test the other? I want to mock self.random_number() output for the unit test of plus_one() to have sane code in unit tests. There is a nice post that compares different mocking libraries and concludes (sadly enough) that none of them is really good to stand out from the others.

在阅读这些库的说明时，我唯一了解到的是，我可以模拟方法的唯一方法是将它们移至特征.我在这些库中没有看到任何示例(我查看了其中的4个或5个)，它们在其中测试了与此类似的情况.

The only thing I learned while reading instructions for these libraries is that the only way I can mock methods is by moving them to a trait. I didn't see any example in these libraries (I looked at 4 or 5 of them) where they test a case similar to this.

将这些方法移至特征后(即使原样)，如何模拟random_number来对RngTest::plus_one的输出进行单元测试?

After moving these methods to a trait (even as they are), how do I mock random_number to unit test the output of RngTest::plus_one?

pub trait SomeRng {
    fn random_number(&self) -> u64 {
        let random = 42; // lets pretend it is random
        return random * self.attr;
    }

    fn plus_one(&self) -> u64 {
        return self.random_number() + 1;
    }
}

impl SomeRng for RngTest {}

推荐答案

如何模拟特定方法，但不是在Rust中模拟所有方法?

How to mock specific methods but not all of them in Rust?

正如您已经了解的那样，您不能替换类型上的方法.您唯一可以做的就是将方法移至特征，然后提供该特征的生产和特定于测试的实现.特征的结构方式决定了您可以测试的粒度.

As you have already learned, you cannot replace methods on a type. The only thing you can do is move the methods to a trait and then provide production and test-specific implementations of that trait. How you structure the trait determines the granularity of what you are able to test.

根据您的用例，您也许可以使用默认实现:

Depending on your use case, you might be able to use a default implementation:

trait SomeRng {
    fn random_number(&self) -> u64;

    fn plus_one(&self) -> u64 {
        self.random_number() + 1
    }
}

struct RngTest(u64);
impl SomeRng for RngTest {
    fn random_number(&self) -> u64 {
        self.0
    }
}

#[test]
fn plus_one_works() {
    let rng = RngTest(41);
    assert_eq!(rng.plus_one(), 42);
}

在这里，random_number是必需的方法，但是plus_one具有默认实现.默认情况下，实现random_number将为您提供plus_one.如果您可以更有效地实现plus_one，也可以选择实施.

Here, random_number is a required method, but plus_one has a default implementation. Implementing random_number gives you plus_one by default. You could also choose to implement plus_one if you could do it more efficiently.

真正的大板条箱具有两个特征:

• Rng

pub trait Rng: RngCore { /* ... */ }

RngCore上的自动实现的扩展特征，提供了用于采样值的高级通用方法和其他便捷方法.

An automatically-implemented extension trait on RngCore providing high-level generic methods for sampling values and other convenience methods.

RngCore

RngCore

pub trait RngCore { /* ... */ }

随机数生成器的核心.

The core of a random number generator.

这将实现的核心部分与帮助器方法分开.然后，您可以控制核心并测试助手:

This splits the core interesting parts of the implementation from the helper methods. You can then control the core and test the helpers:

trait SomeRngCore {
    fn random_number(&self) -> u64;
}

trait SomeRng: SomeRngCore {
    fn plus_one(&self) -> u64 {
        self.random_number() + 1
    }
}

impl<R: SomeRngCore> SomeRng for R {}

struct RngTest(u64);
impl SomeRngCore for RngTest {
    fn random_number(&self) -> u64 {
        self.0
    }
}

#[test]
fn plus_one_works() {
    let rng = RngTest(41);
    assert_eq!(rng.plus_one(), 42);
}

这篇关于如何在Rust中模拟特定的方法，但不是全部?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！