无法使用 jest 和 ts-jest 使用静态方法模拟类

Question

我有两个模拟简单求和运算的类。

import SumProcessor from "./SumProcessor";

class Calculator {

  constructor(private _processor: SumProcessor) { }

  sum(a: number, b: number): number {
    return this._processor.sum(a, b)
  }
}

export default Calculator

还有运算处理器。

class SumProcessor {
  sum(a: number, b: number): number {
    return a + b
  }

  static log() {
    console.log('houston...')
  }
}

export default SumProcessor

我正在尝试模拟 SumProcessor 类以使用 jest+ts-jest 编写以下单元测试。

import Calculator from "./Calculator"
import SumProcessor from "./SumProcessor"
import { mocked } from "ts-jest/utils"

jest.mock('./SumProcessor')

describe('Calculator', () => {

  it('test sum', () => {

    const SomadorMock = <jest.Mock>(SumProcessor)
    SomadorMock.mockImplementation(() => {
      return {
        sum: () => 2        
      }
    })
    const somador = new SomadorMock()
    const calc = new Calculator(somador)
    expect(calc.sum(1, 1)).toBe(2)
  })
})

当 SumProcessor 类中存在静态方法时，模拟代码 const SomadorMock = (SumProcessor) 表示以下编译错误：

TS2345: Argument of type '() => jest.Mock<any, any>' is not assignable to parameter of type '(values?: object, option
s?: BuildOptions) => SumOperator'.
      Type 'Mock<any, any>' is missing the following properties from type 'SumOperator...

如果从 SumProcessor 类中删除静态方法，则一切正常。

有人可以帮忙吗？

Answer 1

因为你已经用jest.mock('./SumProcessor'); 模拟了SumProcessor 类，你可以在你想模拟的方法中添加一个间谍，例如： jest.spyOn(SumProcessor.prototype, 'sum').mockImplementation(() => 2);

这样你的测试类看起来像这样：

import Calculator from "./Calculator"
import SumProcessor from "./SumProcessor"

jest.mock('./SumProcessor')

describe('Calculator', () => {

  it('test sum', () => {
    jest.spyOn(SumProcessor.prototype, 'sum').mockImplementation(() => 2);

    const somador = new SumProcessor();
    const calc = new Calculator(somador)
    expect(calc.sum(1, 1)).toBe(2)
  })
})

简单多了，对吧？