Strange behavior in Jest unit tests with mocked modules - missing properties
I'm experiencing an scenario with Jest where my mocked module doesn't seem to retain the structure of the original module. I'm using Jest version 27.0.6 and trying to mock a utility function from a library called `lodash`. My test case looks like this: ```javascript import _ from 'lodash'; jest.mock('lodash', () => ({ ...jest.requireActual('lodash'), // spread original implementation add: jest.fn(), // mock the add function })); test('should call add with correct parameters', () => { const result = _.add(1, 2); expect(result).toBe(3); expect(_.add).toHaveBeenCalledWith(1, 2); }); ``` However, when I run the test, I get the following behavior: `TypeError: _.add is not a function`. It seems like the mocked version of `add` is not being recognized properly. I confirmed that `lodash` is correctly installed (version 4.17.21) and I can see the `add` function exists when I run it in a separate script. I've tried a few different approaches: I initially mocked only the `add` function without spreading the original module, but that just resulted in calls to the real `add` function. I also attempted to mock using `jest.fn().mockImplementation()` but that didn't work either. I've checked my Jest configuration in `jest.config.js`: ```javascript module.exports = { testEnvironment: 'node', moduleNameMapper: { '^lodash$': '<rootDir>/node_modules/lodash', }, }; ``` This configuration seems correct to me. I want to figure out why the properties of the mocked module are not being retained as expected. Any insights or suggestions would be greatly appreciated.