Javascript 如何使用 Jest 模拟 es6 类
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How to mock es6 class using Jest
提问by dericcain
I am attempting to mock a class Mailerusing jest and I can't figure out how to do it. The docs don't give many examples of how this works. The process is the I will have a node event password-resetthat is fired and when that event is fired, I want to send an email using Mailer.send(to, subject, body). Here is my directory structure:
我正在尝试Mailer使用玩笑来模拟一个课程，但我不知道该怎么做。文档没有给出很多例子来说明这是如何工作的。该过程是我将password-reset触发一个节点事件，当该事件被触发时，我想使用Mailer.send(to, subject, body). 这是我的目录结构：
project_root
-- __test__
---- server
------ services
-------- emails
---------- mailer.test.js
-- server
---- services
------ emails
-------- mailer.js
-------- __mocks__
---------- mailer.js
Here is my mock file __mocks__/mailer.js:
这是我的模拟文件__mocks__/mailer.js：
const Mailer = jest.genMockFromModule('Mailer');
function send(to, subject, body) {
return { to, subject, body };
}
module.exports = Mailer;
and my mailer.test.js
和我的 mailer.test.js
const EventEmitter = require('events');
const Mailer = jest.mock('../../../../server/services/emails/mailer');
test('sends an email when the password-reset event is fired', () => {
const send = Mailer.send();
const event = new EventEmitter();
event.emit('password-reset');
expect(send).toHaveBeenCalled();
});
and finally my mailer.jsclass:
最后是我的mailer.js课：
class Mailer {
constructor() {
this.mailgun = require('mailgun-js')({
apiKey: process.env.MAILGUN_API_KEY,
domain: process.env.MAILGUN_DOMAIN,
});
}
send(to, subject, body) {
return new Promise((reject, resolve) => {
this.mailgun.messages().send({
from: 'Securely App <[email protected]>',
to,
subject: subject,
html: body,
}, (error, body) => {
if (error) {
return reject(error);
}
return resolve('The email was sent successfully!');
});
});
}
}
module.exports = new Mailer();
So, how do I successfully mock and test this class, using Jest? Many thanks for helping!
那么，我如何使用 Jest 成功地模拟和测试这个类？非常感谢您的帮助！
采纳答案by Andreas K?berle
You don't have to mock your mailer class but the mailgun-jsmodule. So mailgun is a function that returns the function messagesthat return the function send. So the mock will look like this.
您不必模拟邮件程序类，而是模拟mailgun-js模块。所以mailgun是一个返回函数的函数messages，返回函数send。所以模拟看起来像这样。
for the happy path
为了幸福的道路
const happyPath = () => ({
messages: () => ({
send: (args, callback) => callback()
})
})
for the error case
对于错误情况
const errorCase = () => ({
messages: () => ({
send: (args, callback) => callback('someError')
})
})
as you have this 2 cases it make sense to mock the module inside your test. First you have to mock it with a simple spy where we later can set the implementation for our cases and then we have to import the module.
由于您有这两种情况，因此在测试中模拟模块是有意义的。首先，您必须使用一个简单的 spy 来模拟它，然后我们可以为我们的案例设置实现，然后我们必须导入模块。
jest.mock('mailgun-js', jest.fn())
import mailgun from 'mailgun-js'
import Mailer from '../../../../server/services/emails/mailer'
As your module uses promises we have 2 options either return the promise from the test or use async/await. I use the later one for more info have a look here.
当您的模块使用 promise 时，我们有 2 个选项可以从测试中返回 promise 或使用async/await. 我使用后一个了解更多信息，请看这里。
test('test the happy path', async() => {
//mock the mailgun so it returns our happy path mock
mailgun.mockImplementation(() => happyPath)
//we need to use async/awit here to let jest recognize the promise
const send = await Mailer.send();
expect(send).toBe('The email was sent successfully!')
});
If you would like to test that the mailgun sendmethod was called with the correct parameter you need to adapt the mock like this:
如果您想测试是否send使用正确的参数调用了 mailgun方法，您需要像这样调整模拟：
const send = jest.fn((args, callback) => callback())
const happyPath = () => ({
messages: () => ({
send: send
})
})
Now you could check that the first parameter for send was correct:
现在您可以检查发送的第一个参数是否正确：
expect(send.mock.calls[0][0]).toMatchSnapshot()
回答by Justus Romijn
Just for Googlers and future visitors, here's how I've setup jest mocking for ES6 classes. I also have a working example at github, with babel-jest for transpiling the ES module syntax so that jest can mock them properly.
仅针对 Google 员工和未来的访问者，以下是我为 ES6 类设置玩笑模拟的方法。我在 github 上也有一个工作示例，使用 babel-jest 来转换 ES 模块语法，以便 jest 可以正确模拟它们。
__mocks__/MockedClass.js
__mocks__/MockedClass.js
const stub = {
someMethod: jest.fn(),
someAttribute: true
}
module.exports = () => stub;
Your code can call this with new, and in your tests you can call the function and overwrite any default implementation.
您的代码可以使用 new 调用它，并且在您的测试中您可以调用该函数并覆盖任何默认实现。
example.spec.js
例子.spec.js
const mockedClass = require("path/to/MockedClass")();
const AnotherClass = require("path/to/AnotherClass");
let anotherClass;
jest.mock("path/to/MockedClass");
describe("AnotherClass", () => {
beforeEach(() => {
mockedClass.someMethod.mockImplementation(() => {
return { "foo": "bar" };
});
anotherClass = new AnotherClass();
});
describe("on init", () => {
beforeEach(() => {
anotherClass.init();
});
it("uses a mock", () => {
expect(mockedClass.someMethod.toHaveBeenCalled();
expect(anotherClass.settings)
.toEqual(expect.objectContaining({ "foo": "bar" }));
});
});
});
