不可能使用 jest 和 ts-jest 用靜態方法模擬類

Question

我有兩個類來模擬簡單的求和運算。

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

和操作處理器。

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

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

export default SumProcessor

我正在嘗試模擬 SumProcessor 類以使用 jest+ts-jest 編寫以下單元測試。

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)
  })
})

當類 SumProcessor 中存在靜態方法時，模擬代碼 const SomadorMock = (SumProcessor) 指示以下編譯錯誤：

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...

如果從 SumProcessor 類中刪除靜態方法，則一切正常。

有人可以幫忙嗎？

Answer 1

因為你已經用jest.mock('./SumProcessor');了SumProcessor類jest.mock('./SumProcessor'); 你可以在你想要模擬的方法中添加一個間諜，例如： jest.spyOn(SumProcessor.prototype, 'sum').mockImplementation(() => 2);

這樣你的測試類看起來像這樣：

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)
  })
})

簡單多了，對吧？