如何开玩笑地模拟函数

Question

我有下面的打字稿类，我想测试在笑话。

//MyClass.ts
import { foo } from './somewhere/FooFactory';
export class MyClass {
  private _state : number;
  constructor( arg : string ) {
    this._state = foo( arg );
  }

  public getState() : string {
    return this._state;
  }
}

这是我的测试：

//MyClass.spec.ts
import { MyClass } from './MyClass';
describe( 'test MyClass', () => {
  test( 'construct' => {
    const c = new MyClass( 'test' );
    expect( c ).toBeDefined();
    expect( c.getState() ).toEqual( 'TEST' );
  } );
} );

如何模拟MyClass中使用的foo函数，以使测试通过？

Answer 1

有几种不同的方法来解决这个问题。

您可以只使用foo使用jest.spyOn和类似于mock实现的东西来模拟foo：

import { MyClass } from './MyClass';
import * as FooFactory from './somewhere/FooFactory';

describe('test MyClass', () => {
  test('construct', () => {
    const mock = jest.spyOn(FooFactory, 'foo');  // spy on foo
    mock.mockImplementation((arg: string) => 'TEST');  // replace implementation

    const c = new MyClass('test');
    expect(c).toBeDefined();
    expect(c.getState()).toEqual('TEST');  // SUCCESS

    mock.mockRestore();  // restore original implementation
  });
});

类似地，您可以使用jest自动模拟foodfactory。mock，然后为foo提供一个实现：

import { MyClass } from './MyClass';
import * as FooFactory from './somewhere/FooFactory';

jest.mock('./somewhere/FooFactory');  // auto-mock FooFactory

describe('test MyClass', () => {
  test('construct', () => {
    const mockFooFactory = FooFactory as jest.Mocked<typeof FooFactory>;  // get correct type for mocked FooFactory
    mockFooFactory.foo.mockImplementation(() => 'TEST');  // provide implementation for foo

    const c = new MyClass('test');
    expect(c).toBeDefined();
    expect(c.getState()).toEqual('TEST');  // SUCCESS
  });
});

您还可以使用传递给jest的模块工厂来模拟FooFactory。模拟：

import { MyClass } from './MyClass';

jest.mock('./somewhere/FooFactory', () => ({
  foo: () => 'TEST'
}));

describe('test MyClass', () => {
  test('construct', () => {
    const c = new MyClass('test');
    expect(c).toBeDefined();
    expect(c.getState()).toEqual('TEST');  // SUCCESS
  });
});

最后，如果您计划在多个测试文件中使用相同的模拟，您可以通过在中创建模拟来模拟用户模块/某处，某处，某处，某处，某处，某处，某处，某处，某处，某处，某处，某处，某处，某处，某处，某处，某处，某处，某处，某处，某处，某处。ts：

export function foo(arg: string) {
  return 'TEST';
}

...然后调用jest.mock（'。/某地/富足工厂'）；在测试中使用模拟：

import { MyClass } from './MyClass';

jest.mock('./somewhere/FooFactory');  // use the mock

describe('test MyClass', () => {
  test('construct', () => {
    const c = new MyClass('test');
    expect(c).toBeDefined();
    expect(c.getState()).toEqual('TEST');  // SUCCESS
  });
});