MRE for https://stackoverflow.com/q/72018137/3001761

app.test.js

const express = require("express");
const request = require("supertest");

const StatusCodes = { CREATED: 201 };
const fakeUserData = {};

const app = express();

it("returns a 201 on successful signup", (done) => {
  request(app)
    .post("/signup")
    .send(fakeUserData)
    .expect(StatusCodes.CREATED)
    .end((err, res) => {
      if (err) {
        return done(err);
      }
      expect(res.body.message).toBe("success");
      return done();
    });
});

// equivalently:
// 
// it("returns a 201 on successful signup", () => {
//   return request(app)
//     .post("/signup")
//     .send(fakeUserData)
//     .expect(StatusCodes.CREATED, { message: "success" });
// });

package.json

{
  "name": "express-supertest",
  "version": "0.1.0",
  "description": "MRE for https://stackoverflow.com/q/72018137/3001761",
  "main": "index.js",
  "scripts": {
    "test": "jest"
  },
  "keywords": [],
  "author": "Jonathan Sharpe <mail@jonrshar.pe>",
  "license": "ISC",
  "devDependencies": {
    "jest": "^28.0.2",
    "supertest": "^6.2.3"
  },
  "dependencies": {
    "express": "^4.18.0"
  }
}