Mocks

Mocking API calls is important not only for testing (which is where it's more often associated), but also during development. It makes you faster at releasing features because it allows you to work in parallel with the team responsible for the API you're calling and it also helps you avoid issues with keeping private keys locally and if the service ever falls over you can continue to develop.
The de-facto standard for mocking API calls in Node.js applications is MSW. MSW is a library that can run in both the browser and on the server and allows you to intercept any request made by your application. It gives you the opportunity to either let the request go through to the original endpoint or to return a mocked response.
Here's a simple example of setting up a mock for an API call (modified) from their docs:
import { http, HttpResponse } from 'msw'
import { setupServer } from 'msw/node'

const server = setupServer(
	// Describe the requests to mock.
	http.get(
		'https://example.com/book/:bookId',
		({ request, params, cookies }) => {
			return HttpResponse.json({
				title: 'Lord of the Rings',
				author: 'J. R. R. Tolkien',
			})
		},
	),
	http.post('/users/:userId', async ({ request, params, cookies }) => {
		const { userId } = params
		const data = await request.json()
		// do something with the data
		return HttpResponse.json({
			id: userId,
			firstName: 'John',
			lastName: 'Maverick',
		})
	}),
)

server.listen({ onUnhandledRequest: 'warn' })
With this set up and running within your server, any request made to a URL matching those patterns will be intercepted by MSW and return a mocked response instead.
πŸ§β€β™‚οΈ Like I said, I already got some things set up for you, so you'll just need to add a mock for the resend email API call. You'll also need to be the one who gets the mocks file imported and sets the right environment variable during development to enable that.
πŸ‘¨β€πŸ’Ό I recommend you start in the file to add the mock, and then set the MOCKS environment variable in , and then finally import the mocks file in .
Once you're done, you should be able to do another test by calling sendEmail from within and you'll see the email that was sent is logged to the console!