使用 jest 框架模拟基类

Question

I have a base class which looks like the following.

class BaseClass {
  .....
  .....
  async request(options) {
    .......
    .......
  }
}

This is extended by another class like this.

const BaseClass = require('@myorg/base-class').BaseClass;

class MyClass extends BaseClass {

      async method1() {
        .............
        request()
        .............
      }

      async method2() {
        .............
        request()
        .............
      }

}

Now I am using jest to test MyClass and it's 2 methods and to mock the BaseClass and trying to send a mocked response for it's request method. Since I need to test both method1 and method2, I need to change the mock return after the first one. I am doing like this.

describe('MyClass', () => {
  afterEach(() => {
    jest.clearAllMocks();
    jest.resetAllMocks();
  });
  let MockClass = class BaseClass {
    request() {
      return {
        statusCode: 200,
        body: JSON.stringify({
          first_response: 'first_response'
        })
      };
    }
  };
  const mock = jest.mock('@myorg/base-class', () => {
    return {
      BaseClass: MockClass
    };
  });
  it('#method1 - test method one', async () => {
    const myClass = require('../src').myClass;
    const res = await myClass.method1();
    expect(res).toEqual('first_response');
  });

  it('#method2 - test method 2', async () => {
    mock.clearAllMocks();
    mock.resetAllMocks();
    MockClass = class BaseClass {
      request() {
        return {
          statusCode: 200,
          body: JSON.stringify({
            random_response: 'random_response'
          })
        };
      }
    };
    const myClass = require('../src').myClass;
    const res = await myClass.method2();
    expect(JSON.parse(res.body)).toEqual({
      random_response: 'random_response'
    });
    expect(res.statusCode).toEqual(200);
  });
});

The problem is once the mock is initialized, I am not able to reset and assign a different value as in the second test. How can I achieve that ?

Answer 1

I had a similar problem a year ago. I had 2 tests calling the same mocked method, but I wished to have 2 differents output.

Jest didn't provide any decent way to modify a mock once it is created, and I assume they didn't change that. (Can't link any source, sorry, it is a while ago).

I had the opportunity to discuss with some experimented and talented programmers, and the work-around was to make the tests in two different files , with 2 implementations for the mock.

Simple, pretty clean if you encounter this problem few times, but not convenient if you have to do this often.

Please let me know if you have a better work-around or a fix!

Good luck