implementing mocking AWS SDK calls in Jest for a Node.js Lambda function
This might be a silly question, but Quick question that's been bugging me - I'm currently working on unit tests for a Node.js Lambda function that interacts with AWS services using the AWS SDK. I've set up Jest for testing, but I'm having trouble effectively mocking the SDK calls, specifically the S3 upload method. Despite using `jest.mock` to mock the `AWS.S3` class, the tests are failing with the following behavior message: `behavior: A promise was not returned from jest.fn()`. Here's a simplified version of my Lambda function: ```javascript const AWS = require('aws-sdk'); const s3 = new AWS.S3(); exports.handler = async (event) => { const params = { Bucket: 'my-bucket', Key: 'my-object', Body: event.body, }; return s3.upload(params).promise(); }; ``` In my test file, I attempted to mock the S3 upload like this: ```javascript const AWS = require('aws-sdk'); const myLambda = require('./myLambda'); jest.mock('aws-sdk', () => { return { S3: jest.fn(() => ({ upload: jest.fn(() => ({ promise: jest.fn().mockResolvedValue('Success') })) })) }; }); test('should upload to S3 and return success message', async () => { const event = { body: 'Test data' }; const response = await myLambda.handler(event); expect(response).toBe('Success'); }); ``` When I run the test, it fails at the `await myLambda.handler(event)` line, and I keep getting the same promise behavior. I've confirmed that the mock setup is correct and that Jest is indeed mocking the AWS SDK, but it seems like the promise is not being handled correctly. I also tried returning a resolved promise directly from the mocked `upload` method, but that didn't resolve the scenario either. Could someone guide to understand why the promise isn't being returned correctly in my mock setup, or suggest a better approach for mocking AWS SDK calls in Jest? This is part of a larger service I'm building. Thanks in advance! My development environment is Windows. Any ideas what could be causing this?