在 Raku 中进行单元测试时如何模拟类方法 [英] How to mock a class method when unittesting in Raku

问题描述

假设我有一个这样的类:

Suppose I have a class like this:

class MyClass {
    method data-is-valid {
        return self!get-data ~~ m{^From};
    }

    method !get-data {
        return 'From Internet';
    }
}

其中 !get-data 方法从 Internet 获取一些数据.

where !get-data method gets some data from Internet.

是否可以模拟该方法，使其返回我自己的硬编码数据，以便我可以在不连接互联网的情况下测试模块?

Is it possible to mock that method so that it returns my own hardcoded data so I can test the module without connecting to the Internet?

理想情况下，解决方案不应以任何方式修改类的定义.

Ideally, the solution should not modify the definition of the class in any way.

注意:类似问题 存在关于模块的单元测试子程序.

NOTE: A similar question exists regarding unittesting subroutines of modules.

推荐答案

我会首先重构以将获取逻辑拉出到不同的对象，并使 MyClass 依赖于它:

I would first refactor to pull the fetching logic out to a different object, and make MyClass depend on it:

class Downloader {
    method get-data {
        return 'From Internet';
    }
}

class MyClass {
    has Downloader $.downloader .= new;

    method data-is-valid {
        return $!downloader.get-data ~~ m{^From};
    }
}

这是一个依赖倒置的例子，它是一种使代码可测试的有用技术(并且倾向于使其更容易以其他方式演化).

This is an example of dependency inversion, which is a helpful technique for making code testable (and tends to make it easier to evolve in other ways too).

通过此更改，现在可以使用 Test::Mock 模块来模拟下载器:

With this change, it is now possible to use the Test::Mock module to mock Downloader:

use Test;
use Test::Mock;

subtest 'Is valid when contains From' => {
    my $downloader = mocked Downloader, returning => {
        get-data => 'From: blah'
    };
    my $test = MyClass.new(:$downloader);
    ok $test.data-is-valid;
    check-mock $downloader,
        *.called('get-data', :1times);
}

subtest 'Is not valid when response does not contain From' => {
    my $downloader = mocked Downloader, returning => {
        get-data => 'To: blah'
    };
    my $test = MyClass.new(:$downloader);
    nok $test.data-is-valid;
    check-mock $downloader,
        *.called('get-data', :1times);
}

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