typescript - 用 Jest 测试 typescript 中的私有(private)函数

Question

在下面的代码中，我的测试用例按预期通过了，但我使用 stryker 进行突变测试，handleError 函数在突变测试中幸存下来，所以我想通过测试是否调用了 handleError 函数来杀死突变体。需要帮助测试私有(private)功能。

我试过 spyOn 但没有用

const orderBuilderSpy = jest.spyOn(orderBuilder, 'build')
const handleError = jest.fn()
expect(rderBuilderSpy).toHaveBeenCalledWith(handleError)

// code written in nestJS/typescript

export class OrderBuilder {
  private amount: number

  public withAmount(amount: number): BuyOrderBuilder {
    this.amount = amount
    return this
  }


  public build(): TransactionRequest {
    this.handleError()
    return {
      amount: this.amount,
      acceptedWarningRules: [
        {
          ruleNumber: 4464
        }
      ]
    }
  }
  private handleError() {
    const errors: string[] = []
    const dynamicFields: string[] = [
      'amount',
    ]
    dynamicFields.forEach((field: string) => {
      if (!this[field]) {
        errors.push(field)
      }
    })
    if (errors.length > 0) {
      const errorMessage = errors.join()
      throw new Error(`missing ${errorMessage} field in order`)
    }
  }

}


// test
describe('Order Builder', () => {
  it('should test the handleError', () => {
    const orderBuilder = new OrderBuilder()
    const errorMessage = new Error(
      `missing amount field in order`
    )
    try {
      orderBuilder.build()
    } catch (error) {
      expect(error).toEqual(errorMessage)
    }
  });
});

Answer 1

您似乎想要验证 handleError在 build 时被调用运行。

私有(private)方法被编译成普通的 JavaScript 原型(prototype)方法，所以你可以使用 any type 让 spy 创建通过 TypeScript 类型检查。

这是一个高度简化的示例:

class OrderBuilder {
  public build() {
    this.handleError()
  }
  private handleError() {
    throw new Error('missing ... field in order')
  }
}

describe('Order Builder', () => {
  it('should test the handleError', () => {
    const handleErrorSpy = jest.spyOn(OrderBuilder.prototype as any, 'handleError');
    const orderBuilder = new OrderBuilder()
    expect(() => orderBuilder.build()).toThrow('missing ... field in order');  // Success!
    expect(handleErrorSpy).toHaveBeenCalled();  // Success!
  });
});