[Express]JestのみでE2Eに近いテスト

index.ts

import express from "express";
import hello from "./hello";

const app = express();
app.use(express.json());
app.use(express.urlencoded({ extended: true }));

app.get("/", hello);

const port = process.env.PORT || 4000;
app.listen(port, () => {
  const url = `http://localhost:${port}`;
  console.log(`------------------------------------------------------`);
  console.log(`🚀 Server ready at ${url}`);
  console.log(`------------------------------------------------------`);
});

hello.ts

import { Request, Response } from "express";

const hello = (req: Request, res: Response) => {
  return res.status(200).json({ message: "Hello World!" });
};

export default hello;

hello.test.ts

import { Request, Response } from "express";
import hello from "./hello";

it("Hello World!", async () => {
  const req = {} as Request;
  const res = {
    status: jest.fn().mockReturnThis(),
    json: jest.fn().mockReturnThis(),
  } as jest.MockedObject<Response>;
  hello(req, res);
  expect(res.status.mock.calls[0][0]).toBe(200);
  expect(res.json.mock.calls[0][0]).toEqual({ message: "Hello World!" });
});