Testing behavior in Express

app.js

import express from "express"
import {behavior1} from "./behavior.js"

var app = express();

app.use(function (req, res, next) {
  behavior1()
    .then(res.send.bind(res))
    .catch(next);
});

app.listen(3000);

async-request-mock.js

export function asyncRequest () {
    return new Promise((resolve, reject) => {
      process.nextTick(() => {
        resolve('Hello World');
      });
    });
};

behavior-spec.js

import Assert from "assert"
import {behavior1} from "./behavior.js"

describe('behavior', () => {
  describe('behavior1', () => {
    it('returns "Hello World"', () => {
      return behavior1().then((body) => {
        Assert.equal(body, 'Hello World');
      });
    });
  });
});

behavior.js

import {asyncRequest} from "./async-request-mock.js"

export function behavior1 () {
  return asyncRequest();
}