import { EventEmitter } from 'events' import { getFreePort } from "./port" jest.mock("net", () => { return { createServer() { return new class MockServer extends EventEmitter { listen = jest.fn(() => { this.emit('listening') return this }) address = () => { return { port: 12345 } } unref = jest.fn() close = jest.fn(cb => cb()) } }, } }); describe("getFreePort", () => { it("finds the next free port", async () => { return expect(getFreePort()).resolves.toEqual(expect.any(Number)) }) })