How to make typescript working with mocked ES6 class extra static properties with Jest?

Question

I have created a mock file for mangopay2-nodejs-sdk in order to simulate payment failure for my Jest tests:

// __mocks__/mangopay2-nodejs-sdk.ts
import BaseMangoPay from 'mangopay2-nodejs-sdk';

export default class MangoPay extends BaseMangoPay {
  static __willFail: boolean = false;

  constructor(config: BaseMangoPay.Config) {
    super(config);

    // Mocked stuff.

    this.CardPreAuthorizations = {
      create: (
        data: cardPreAuthorization.CreateCardPreAuthorization,
      ): Promise<cardPreAuthorization.CardPreAuthorizationData> => Promise.resolve({
        ...data,
        Id: '1337',
        Status: MangoPay.__willFail ? 'FAILED' : 'SUCCEEDED',
      }),
    };
  }
}

Note: The original import is a class that has to be instantiated with a configuration to work properly.

I added an extra __willFail static property to make my mock failing when I want on my tests:

import MangoPay from 'mangopay2-nodejs-sdk';

describe('payment failures', () => {
  beforeEach(() => {
    MangoPay.__willFail = true;
  });
  afterAll(() => {
    MangoPay.__willFail = false;
  });

  // The tests.
});

This is working perfectly fine. However, typescript does not recognize the __willFail extra static property of my mocked class:

Property '__willFail' does not exist on type 'typeof MangoPay'.ts(2339)

I expected this error of course, but I don't know how to solve it.

I found similar answers like this one: https://stackoverflow.com/a/53222290/1731473

But this is working with imported variable.

How can I apply this kind of method to make Typescript working with my extra static property?

The answer you linked shows the exact way how it's done. You need to import MockMangoPay from __mocks__ just to do (MangoPay as typeof MockMangoPay).__willFail. — Estus Flask
The difference is the example show a ready to use imported object. Here, I have to instantiate the MangoPay instance on the source code (not on test thanks to static property). — Soullivaneuh
I am currently stuck about how to manage with imports and I don't need to instanciate the instance on tests. I just need TS to check the right typing. May you give a complete example on the answer? :-) — Soullivaneuh

Estus Flask Estus Flask · Accepted Answer · 2021-01-18T08:03:05

The approach described in this answer is applicable to this case. There needs to be a separate type import for type assertions:

import MangoPay from 'mangopay2-nodejs-sdk';
import MockMangoPay from '.../__mocks__/mangopay2-nodejs-sdk'; 
...    
(MangoPay as typeof MockMangoPay).__willFail = true;

Without that, type safety needs to be disabled, which can be acceptable for one-off use in tests:

(MangoPay as any).__willFail = true;

How to make typescript working with mocked ES6 class extra static properties with Jest?

1 Answers