How to effectively mock dependencies in Jest for nested async functions?
I'm a bit lost with After trying multiple solutions online, I still can't figure this out... I've been struggling with this for a few days now and could really use some help. I'm converting an old project and Hey everyone, I'm running into an issue that's driving me crazy. This might be a silly question, but I'm currently working on a Node.js application using Jest for unit testing, and I'm struggling with mocking dependencies for a function that has nested asynchronous calls. I have a service that fetches user data and then processes it, which involves a call to an external API. Here's a simplified version of the code: ```javascript const axios = require('axios'); class UserService { async fetchUser(userId) { const response = await axios.get(`https://api.example.com/users/${userId}`); return this.processUser(response.data); } processUser(data) { // Imagine some complex processing here return {...data, processed: true}; } } module.exports = UserService; ``` In my test, I want to mock the `axios.get` method to avoid hitting the actual API and to control the response. I tried the following, but I'm getting an behavior that says `TypeError: want to read property 'data' of undefined` when I call `processUser`: ```javascript const UserService = require('./UserService'); const axios = require('axios'); jest.mock('axios'); describe('UserService', () => { it('should fetch and process user data', async () => { const userService = new UserService(); const mockUserData = { id: 1, name: 'John Doe' }; axios.get.mockResolvedValue({ data: mockUserData }); const result = await userService.fetchUser(1); expect(result).toEqual({ ...mockUserData, processed: true }); }); }); ``` I am unsure why the mocking setup isn't working as expected. Could it be because of how the `fetchUser` method accesses the response? Any guidance on best practices for mocking in Jest, especially when dealing with nested async functions, would be greatly appreciated. I'm using Jest version 27.0.6 and Node.js version 14.17.0. I'm working on a application that needs to handle this. I'm working on a CLI tool that needs to handle this. What's the best practice here? I'm working in a macOS environment. What's the best practice here? What's the correct way to implement this? The project is a web app built with Javascript. Has anyone dealt with something similar? I'd really appreciate any guidance on this.