Jest/Typescript：模擬 class 依賴項，其中包含 jest 和 typescript 中的私有成員

Question

Context: I have class B which is dependent on class A. I want to test a method of class B which is internally calling a method of class A. Now, I want to unit test my method of class B by mocking class A.

注 1 ： Class A 有一些私有成員

注2 ： Class A無接口

這是我的代碼結構：

class Base {

  someMethod() {
     return "Hello ";
  }

}


class A {

  private _baseClassImpl: Base;

  constructor(baseClassImpl: Base) {
     this._baseClassImpl = baseClassImpl;
  }

  getSomething() {     
     return this._baseClassImpl.someMethod() + " Something";
  }
}


class B {
  constructor(objectOfClassA: A) {
      this._objectOfClassA = objectOfClassA;

 }

 functionOfClassBToTest() {
     const returnValueFromClassA = this._objectOfClassA.getSomething();

     return returnValueFromClassA;
 }
}

到目前為止我已經嘗試過：

從我之前的 SO 帖子中獲得建議后，我嘗試編寫如下測試：

const getSomethingMock = jest.fn().mockImplementation(() => {
    return "Mock value";
});

const mockA = jest.Mocked<A> = {
   getSomething: getSomethingMock
};

test("test functionOfClassBToTest", () => {
   const classBToTest = new B(mockA);
   
   expect(classBToTest.functionofClassBToTest.toStrictEqual("Hello Something");

});

上面的代碼給了我這個錯誤：

Type '{ getSomething: jest.Mock<any, any>; }' is not assignable is not assignable to type 'Mocked<A>'. 
Type '{ getSomething: jest.Mock<any, any>; }' is missing the following properties from type 'A': _baseClassImpl

當我嘗試像這樣為 _baseClassImpl 提供模擬值時：

const baseClassMock = jest.Mocked<Base> = {
  someMethod: jest.fn()
};

const getSomethingMock = jest.fn().mockImplementation(() => {
    return "Mock value";
});

const mockA = jest.Mocked<A> = {
   getSomething: getSomethingMock,
   _baseClassImpl: baseClassMock
};

Typescript 給了我這個錯誤：

Type '{ getSomething: jest.Mock<any, any>; _baseClassImpl: jest.Mocked<Base>; }' is not assignable is not assignable to type 'Mocked<A>'. 

Type '{ getSomething: jest.Mock<any, any>; _baseClassImpl: jest.Mocked<Base>; }' is not assignable is not assignable to type 'A'. 

Property '_baseClassImpl' is private in type 'A' but not in type '{ getSomething: jest.Mock<any, any>; _baseClassImpl: jest.Mocked<Base>; }'

我已經在我之前的 SO 帖子中嘗試過答案，但它在 class 與私人成員的情況下不起作用。

一些注意事項：

注 1 ： Class A 包含私有成員

注2 ： Class A無接口

注 3 ：我不想在我的測試 function 中初始化 class A 的 object。 我只想模擬 class。

Answer 1

通過這個github repo的一些嘗試和幫助，我能夠解決這個問題。

這是供參考的代碼：

測試 functionOfClassBToTest：

//Note: this can be also written as : const mockA = new (<any>A)() as jest.Mocked<A>;
const mockA = new (<new () => A>A)() as jest.Mocked<A>;

mockA.getSomething = jest.fn();

test("test functionOfClassBToTest", () => {
   
   mockA.getSomething.mockReturnValueOnce("Hello Something");

   const classBToTest = new B(mockA);
   
   expect(classBToTest.functionofClassBToTest.toStrictEqual("Hello Something");

});