Testing Real-Time Systems — Real-Time APIs

Test protocol handlers as units (message in → messages out), run integration tests with real WebSocket clients against a test server, and load test connections: concurrent connections, message fan-out rates, reconnect storms and slow consumers (k6, Artillery, Gatling support WebSockets). Inject network faults (latency, drops) to verify resync logic, and test deploy draining.

Real-time test plan

Test	Verifies
Protocol unit tests	Message handling logic
Integration with real clients	Auth, subscriptions, fan-out
Connection load test	Memory/FD limits, fan-out latency
Reconnect storm test	Admission control, auth capacity
Fault injection	Gap detection and resync

import ws from "k6/ws";
import { check } from "k6";
export const options = { vus: 5000, duration: "10m" };
export default function () {
  const res = ws.connect(`${__ENV.WS_URL}?ticket=${getTicket()}`, {}, (socket) => {
    socket.on("open", () => socket.send(JSON.stringify({ type: "subscribe", channel: `room:${__VU % 100}` })));
    socket.on("message", () => {});
    socket.setInterval(() => socket.send(JSON.stringify({ type: "message", text: "hi" })), 10_000);
    socket.setTimeout(() => socket.close(), 60_000);
  });
  check(res, { "status 101": (r) => r && r.status === 101 });
}

it("delivers room messages to other members", async () => {
  const [a, b] = await Promise.all([connect("alice"), connect("bob")]);
  await Promise.all([a.subscribe("room:1"), b.subscribe("room:1")]);
  a.send({ type: "message", channel: "room:1", text: "hello" });
  expect(await b.next("message")).toMatchObject({ channel: "room:1", text: "hello" });
});

Common pitfalls

Load testing only HTTP RPS.
Never testing reconnect storms.
Mocking the socket layer in every test.

Key points

Real clients in integration tests
Load test connections and fan-out
Inject faults to test resync

Real-time test plan

Common pitfalls

Key points

Practice questions