Support for server-only testing NextJS App Router Server Actions

[aniketbiprojit]

Goals

1. A required toolkit which automatically mocks functions like cookies, headers, NextRequest and NextResponse if an env flag is passed.
2. jest.mock even fails if an import exists from 'next/headers'. So allow mocks for above with a env flag.

Non-Goals

No response

Background

Not able to run e2e test on server actions due to these limitations.

If I import a server action without running next this is the current error:

Error [ERR_MODULE_NOT_FOUND]: Cannot find module '/node_modules/next/headers' imported from src/server/login.ts
Did you mean to import [email protected]_@[email protected][email protected][email protected][email protected]/node_modules/next/headers.js?

Current alternative for mocking cookies:

type TestCookie = {
  name: string;
  value: string;
  expires?: Date;
  httpOnly?: boolean;
};

type ReturnCookieType = {
  get: (name: string) =>
    | {
        name: string;
        value: string;
      }
    | undefined;

  set: (
    ...args:
      | [
          key: string,
          value: string,
          options: Omit<TestCookie, "name" | "value">,
        ]
      | [options: TestCookie]
  ) => unknown;
};

class TestCookies {
  static _cookie_value = new Map<string, string>();

  static get(name: string) {
    const _cookie_value = TestCookies._cookie_value.get(name);

    if (_cookie_value) {
      return {
        name: name,
        value: _cookie_value,
      };
    }
  }

  static set(
    ...args:
      | [
          key: string,
          value: string,
          options: Omit<TestCookie, "name" | "value">,
        ]
      | [options: TestCookie]
  ) {
    if (typeof args[0] === "string" && args[1]) {
      TestCookies._cookie_value.set(args[0], args[1]);
      return {
        name: args[0],
        value: args[1],
      };
    } else {
      const name = (args[0] as TestCookie).name;
      const value = (args[0] as TestCookie).value;
      TestCookies._cookie_value.set(name, value);

      return {
        name: name,
        value: value,
      };
    }
  }
}

export const getCookies = async (): Promise<ReturnCookieType> => {
  if (env.NODE_ENV === "test") {
    return TestCookies;
  }
  const { cookies } = await import("next/headers");

  const nextHeaders = cookies();
  return nextHeaders;
};

Proposal

Automatic mocking of these requests would be pretty good for a flag like MOCK_NEXT_FUNCTIONS="true".

Or allow import of next/headers to be allowed so we can directly use jest.mock and not update cookies() -> await getCookies() everywhere.