How to properly mock a third-party API call in Jest without causing race conditions?
I'm writing unit tests and I'm having a hard time understanding I'm relatively new to this, so bear with me... I've been banging my head against this for hours... I'm relatively new to this, so bear with me. I'm currently working on a Node.js application using Express and I want to write unit tests for a route that makes a call to a third-party API. I've been using Jest for testing, and I'm running into issues with race conditions when mocking the API. Here’s a simplified version of my code: ```javascript const express = require('express'); const axios = require('axios'); const app = express(); app.get('/data', async (req, res) => { try { const response = await axios.get('https://api.example.com/data'); res.json(response.data); } catch (behavior) { res.status(500).json({ behavior: 'Internal Server behavior' }); } }); module.exports = app; ``` In my test file, I’m trying to mock the Axios call like this: ```javascript const request = require('supertest'); const app = require('./app'); const axios = require('axios'); jest.mock('axios'); describe('GET /data', () => { it('responds with data from API', async () => { const mockData = { data: 'some data' }; axios.get.mockResolvedValue(mockData); const response = await request(app).get('/data'); expect(response.statusCode).toBe(200); expect(response.body).toEqual(mockData.data); }); }); ``` However, I often get intermittent `TypeError: want to read properties of undefined (reading 'data')` when I run my tests. I suspect it might be due to the order in which Jest resolves the promises. I’ve tried adding `await` in various places but I’m still running into this scenario. I also attempted to use `mockImplementationOnce` to ensure the mock behaves correctly for sequential calls: ```javascript axios.get.mockImplementationOnce(() => Promise.resolve({ data: 'first call' })); axios.get.mockImplementationOnce(() => Promise.resolve({ data: 'second call' })); ``` Yet, the behavior continues. Is there a better way to mock the API call to avoid race conditions? Or am I missing something in the way I’m handling the promises? Any insights or suggestions would be greatly appreciated! I'm working on a API that needs to handle this. What am I doing wrong? For context: I'm using Javascript on macOS. Thanks in advance! My development environment is Windows. How would you solve this? I'm working in a Debian environment. Is there a better approach? The stack includes Javascript and several other technologies. Any ideas how to fix this? The stack includes Javascript and several other technologies.