In my case, I had to mock a Node.js module. I'm using React and Redux in ES6, with Jest and Enzyme for unit tests.

In the file I'm using, and writing a test for, I'm importing the node modules as default:

import nodeModulePackage from 'nodeModulePackage';

So I needed to mock it as a default since I kept getting the error (0, _blah.default) is not a function..

My solution was to do:

jest.mock('nodeModulePackage', () => jest.fn(() => {}));

In my case, I just needed to override the function and make it return an empty object.

If you need to call a function on that node module, you'll do the following:

jest.mock('nodeModulePackage', () => ({ doSomething: jest.fn(() => 'foo') }));

It looks like the reason why you're getting this error has to do with the data you're mocking through Jest.

Try using jest.fn() to mock your getIdToken as a function, rather than a string:

const mockGetIdToken = jest.fn(() => 'abc123');

jest.mock('services/firebase', () => new Promise(resolve => resolve({
  signInWithEmailAndPassword: () => Promise.resolve({ getIdToken: mockGetIdToken }),
  getIdToken: mockGetIdToken,
  signOut: () => jest.fn()
})));

describe('login actions', () => {
  let store;

  beforeEach(() => {
    store = mockStore({});
  });

  it('signIn should call firebase', () => {
    const user = {
      email: '[email protected]',
      password: 'abd123'
    };

    return store.dispatch(signIn(user.email, user.password))
      .then(() => {
        console.log('TEST signIn SUCCESS');
        expect(mockSignIn).toHaveBeenCalled();
        expect(store.getActions()).toEqual({
          type: USER_ON_LOGGED_IN
        });
      })
      .catch((err) => {
        console.log('TEST signIn ERROR =>', err);
      });
  });

You need to do 'export default' in the sum function if you want to import the function without unpacking. Otherwise, you need to unpack when importing like 'import {sum} from...'

Jest by default does not support testing Accessibility.

You will need to make sure you use the Salesforce Accessibility Automation Libraries

We have a blog post detailing how to setup and get started with it.

Key Steps are as follows

1. Make sure to Install @sa11y/jest as dev dependency.

   npm install -D @sa11y/jest

2. Create a setup file that registers the toBeAccessible() sa11y matcher so that it can be used with expect()

You will need a file named jest-sa11y-setup.js with below code

import { registerSa11yMatcher } from '@sa11y/jest';

registerSa11yMatcher();

3. Include the newly created setup file into your generic jest config file. So your jest.config.js file should look like below

    const { jestConfig } = require('@salesforce/sfdx-lwc-jest/config');
   
   const setupFilesAfterEnv = jestConfig.setupFilesAfterEnv || [];
   setupFilesAfterEnv.push('<rootDir>/jest-sa11y-setup.js');
   
   module.exports = {
       ...jestConfig,
       setupFilesAfterEnv
   };
   

Once you have all the above your Jest code should work fine.

The jest object is automatically in scope within every test file, so there's no need to import it explicitly. If you do want to import the jest object directly, you want to import the jest-mock module, not the jest-cli module, via:

// Not necessary inside a Jest test file
import jest from 'jest-mock';

const mock = jest.fn();

automock is a bad practice and should be preferably disabled. In case a module needs to be automatically mocked, this can be done explicitly with jest.mock. Manual mocks are preferable most times because they result in explicitly specified implementations that should be additionally provided to auto-mocks, too.

Jest auto-mocking is undocumented, it results in poorly understood magic that may not meet the expectations of a developer and may change without notice in next Jest versions. Class auto-mocking is briefly described in the guide. getAllData is instance method that is created inside a constructor. Jest auto-mocking relies on runtime contents of a module and checks static and prototype members, there's no way how it could process a constructor.

In order to be detected by Jest auto-mocking, getAllData should be prototype method, this is also suggested by common sense because there are no reasons for it to be an arrow:

export class TestService {
    getAllData(): Promise<any> {
        return { id: '1', name: 'test' }
    }
}

Auto-mocking doesn't result in a correct mock because the method is stubbed it doesn't return a promise. The problem could be determined at earlier point because auto-mocks require an implementation to be specified, this wasn't done in the OP:

const service = new TestService();
service.getAllData.mockResolvedValueOnce(...);
...

For prototype methods this can be done before an instance is available:

TestService.prototype.getAllData.mockResolvedValueOnce(...);
const service = new TestService();
...

Remove this line:

import { test, expect } from 'jest'

You don't need to import anything from Jest. See example.

restart metro bundler with yarn start or npm start solved my problem

I take it you're using ts-jest?

replace

import { it, before, describe } from 'jest';

with

import 'jest';