如何使用mocha.js模拟单元测试的依赖类？ [英] How to mock dependency classes for unit testing with mocha.js?

问题描述

鉴于我有两个ES6课程。

Given that I have two ES6 classes.

这是A类：

import B from 'B';

class A {
    someFunction(){
        var dependency = new B();
        dependency.doSomething();
    }
}

和B类：

class B{
    doSomething(){
        // does something
    }
}

我使用mocha进行单元测试（使用babel for ES6），chai和sinon，效果非常好。但是我怎样才能在测试A类时为B类提供一个模拟类？

I am unit testing using mocha (with babel for ES6), chai and sinon, which works really great. But how can I provide a mock class for class B when testing class A?

我想模拟整个B类（或者所需的函数，实际上并不重要） ）所以A类不执行实际代码，但我可以提供测试功能。

I want to mock the entire class B (or the needed function, doesn't actually matter) so that class A doesn't execute real code but I can provide testing functionality.

这就是现在的mocha测试：

This is, what the mocha test looks like for now:

var A = require('path/to/A.js');

describe("Class A", () => {

    var InstanceOfA;

    beforeEach(() => {
        InstanceOfA = new A();
    });

    it('should call B', () => {
        InstanceOfA.someFunction();
        // How to test A.someFunction() without relying on B???
    });
});

推荐答案

您可以使用SinonJS创建stub 以防止执行实际功能。

You can use SinonJS to create a stub to prevent the real function to be executed.

例如，给定A类：

import B from './b';

class A {
    someFunction(){
        var dependency = new B();
        return dependency.doSomething();
    }
}

export default A;

B类：

class B {
    doSomething(){
        return 'real';
    }
}

export default B;

测试结果如下：

describe("Class A", () => {

    var InstanceOfA;

    beforeEach(() => {
        InstanceOfA = new A();
    });

    it('should call B', () => {
        sinon.stub(B.prototype, 'doSomething', () => 'mock');
        let res = InstanceOfA.someFunction();

        sinon.assert.calledOnce(B.prototype.doSomething);
        res.should.equal('mock');
    });
});

然后，如果需要，您可以使用 object.method.restore恢复该功能（ ）; ：

You can then restore the function if necessary using object.method.restore();:

var stub = sinon.stub（object，method）;

用
存根函数替换object.method。可以通过调用
object.method.restore（）; （或 stub.restore（）; ）。如果属性不是函数，则抛出
异常，以帮助避免在
存根方法时出现拼写错误。

var stub = sinon.stub(object, "method");
Replaces object.method with a stub function. The original function can be restored by calling object.method.restore(); (or stub.restore();). An exception is thrown if the property is not already a function, to help avoid typos when stubbing methods.

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