嘲笑具有DI依赖关系的类 [英] Jest mocking of classes with DI dependencies

问题描述

各种Jest文档显示了自动"模拟，手动"模拟或

Various Jest docs show creation of "automatic" mocks, "manual" mocks, or ES6 class mocks (which instantiate dependencies within the constructor).

但是我想使用DI/IOC并将依赖项注入ctor:

But I want to use DI / IOC and inject dependencies into the ctor:

// IBar.ts                                           <--- mock this
export default interface IBar {
  /* ...methods... */
}

// Baz.ts                                            <--- mock this
export default class Baz {
  constructor(spam: Spam, ham: IHam) { /* ... */}
  /* ...other methods... */
}

// Foo.ts                                            <--- test this
export default class Foo {
  constructor(bar: IBar, baz: Baz) { /* ... */}
  /* ...other methods... */
}

所以我想在测试中做到这一点:

So I want to do this in a test:

const barMock = jest.giveMeAMock("../../IBar");  // or jest.giveMeAMock<IBar>();
const bazMock = jest.giveMeAMock("./Baz");       // or jest.giveMeAMock<Baz>();
const foo = new Foo(bar, baz);

expect(foo.something()).toBe(true);

Jest有可能吗?

(我在上面使用了一些TypeScript语法，但是对于JS/ES6和TS来说是同样的问题.)

(I used some TypeScript syntax above, but it's the same problem for JS/ES6 and TS.)

推荐答案

当代码转换为JavaScript时，TypeScript接口只是被编译掉了.

TypeScript interfaces just get compiled away when the code gets converted to JavaScript...

...但是class绝对有可能.

...but it's definitely possible for a class.

您可以使用jest.mock自动模拟模块，并且Jest将使模块的API表面保持相同，同时用空的

You can auto-mock a module using jest.mock and Jest will keep the API surface of the module the same while replacing the implementation with empty mock functions:

baz.js

export default class Baz {
  doSomething() {
    throw new Error('the actual function throws an error');
  }
}

foo.js

export default class Foo {
  constructor(baz) {
    this.baz = baz;
  }
  doSomething() {
    // ...
    this.baz.doSomething();
    // ...
  }
}

code.test.js

code.test.js

jest.mock('./baz');  // <= auto-mock the module

import Baz from './baz';
import Foo from './foo';

test('Foo', () => {
  const baz = new Baz();  // <= baz is an auto-mocked instance of Baz
  const foo = new Foo(baz);

  foo.doSomething();  // (no error)

  expect(baz.doSomething).toHaveBeenCalled();  // Success!
})

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