Async support wrapper for node-mocks-http, allows to write unit tests for next.js api pages

api.nextjs.test.ts

import { createMocksAsync } from '../../../utils/node-mocks-http';
// nextjs handler
import logout from '../../../pages/api/auth/logout';

describe('logout api', () => {
  it('should clear cookies and redirect to home', async () => {

    const refreshToken = 'refresh_token_1';
    const { req, res, result } = createMocksAsync({
      method: 'GET',
      url: '/api/auth/logout',
      cookies: {
        token: 'token_1',
      },
    });

    // @ts-ignore
    logout(req, res);

    await result;
    
    // expect something 
  });
});

node-mocks-http.ts

/* eslint-disable no-underscore-dangle */
import { Request, Response } from 'express';
import httpMocks, {
  MockRequest,
  MockResponse,
  RequestOptions,
  ResponseOptions,
} from 'node-mocks-http';
// const httpMocks = require('node-mocks-http');

export interface Mocks<T1 extends Request, T2 extends Response> {
  req: MockRequest<T1>;
  res: MockResponse<T2>;
  result: Promise<Array<any>>;
  err: any;
}

// eslint-disable-next-line global-require
httpMocks.createResponse({ eventEmitter: require('events').EventEmitter });

// this wrapper allows to wait for async handlers which is not supported by default
export function createMocksAsync<T1 extends Request = Request, T2 extends Response = Response>(
  reqParams?: RequestOptions,
  resParams?: ResponseOptions
): Mocks<T1, T2> {
  let errResolver;
  const error = new Promise((res) => {
    errResolver = res;
  });

  const { req, res } = httpMocks.createMocks<T1, T2>(reqParams, resParams);

  let dataResolver: (data: object) => void | null;
  const data = new Promise((resolve) => {
    dataResolver = resolve;
  });
  res.on('end', () => dataResolver(res._getData()));

  const result = Promise.race([Promise.all([error, null]), Promise.all([null, data])]);
  return { req, res, err: errResolver, result };
}