How can I mock Next.js API functions for unit tests?

Question

I want to mock some of these functions for unit tests of my library. More specifically, cookies and headers functions must be present, because my library integrates with Next-Auth.

Next.js API reference: https://nextjs.org/docs/app/api-reference/functions
Next-Auth: https://next-auth.js.org/configuration/nextjs

According to the Next-Auth docs, we should be able to use getServerSession inside React Server Components or API Routes.

import { getServerSession } from "next-auth/next"
import { authOptions } from "pages/api/auth/[...nextauth]"

export default async function Page() {
  const session = await getServerSession(authOptions)
  return <pre>{JSON.stringify(session, null, 2)}</pre>
}

However, when I checked the source code of Next-Auth, I couldn't find unit tests that specifically targets React Server Components, which makes me wonder whether mocking all these functions is ever possible

{JSON.stringify(session, null, 2)}

}However, when I checked the source code of Next-Auth, I couldn't find unit tests that specifically targets React Server Components, which makes me wonder whether mocking all these functions is ever possible

Matt · Answer

Have you tried something like this?const mockCookies = jest.fn();
jest.mock('next/headers',  () => (
   {
      cookies: mockCookies
   })
);

. . .

it("should return cookies", () = > {
   mockCookies.mockReturnedValue = {
      . . .
   };
});My syntax may be a little off, so you may want to double check it. In essence, I think because they're modules you should be able to mock them as such in Jest.Here are some links you may find useful on how to mock modules in Jest, if you're not familiar:- Mock entire module -  https://jestjs.io/docs/mock-functions#mocking-modules- Mock part of a module - https://jestjs.io/docs/mock-functions#mocking-partials

How can I mock Next.js API functions for unit tests?

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