⚡ QuickStart

⚡ QuickStart with @fizzwiz/mockchain

“Test the network one node at a time — by mocking one Promise at a time.”

This QuickStart guide shows you how to use @fizzwiz/mockchain to make asynchronous operations fully mockable — ideal for testing distributed nodes, event-driven systems, or networked applications.

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1. Installation

Install via npm:

npm install @fizzwiz/mockchain

Or via yarn:

yarn add @fizzwiz/mockchain

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2. Basic Usage

Wrap your Promises in MockChain to make them mockable.

import { MockChain } from '@fizzwiz/mockchain';

// In your code
function doFetch(url, autoStart = true) {
  const chain = MockChain.from(fetch(url), autoStart)
    .then(res => res.json());
  return chain; // returns MockChain<Response, Object>
}

// In your test
const fetchChain = doFetch('https://example.com', false);
fetchChain.root.mock(new Response(JSON.stringify({ ok: true })));
const obj = await fetchChain; // await the result

This simulates a network response without sending a real request.

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3. Mocking WebSocket Messages

Simulate WebSocket messages easily:

import { MockChain } from '@fizzwiz/mockchain';

// In code
function sendAndReceive(webSocket, request) {
  if (request) webSocket.send(request);
  const wsChain = MockChain.fromMessage(webSocket, () => true, false, !!request)
    .then(msg => console.log(msg.data));
  return wsChain;
}

// In test
const wsChain = sendAndReceive(undefined, undefined);
wsChain.root.mock({ data: 'mocked message' }); // trigger the chain from root
// -> 'mocked message'

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4. Mocking Generic Events

Wrap any EventEmitter or EventTarget event in a mockable chain:

import { MockChain } from '@fizzwiz/mockchain';

// In code
function triggerAndReact(trigger, emitter, eventName, isEvent) {
  if (trigger) trigger();
  const eventChain = MockChain.fromEvent(emitter, eventName, isEvent)
    .then(data => console.log(data));
  return eventChain;
}

// In test
const eventChain = triggerAndReact(undefined, undefined, () => true);
eventChain.root.mock('mocked event'); // trigger the chain from root
// -> 'mocked event'

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5. Delayed Resolution and Rejection

Simulate network latency or delayed events:

const chain = new MockChain(undefined, false).then(console.log);
chain.root.mockAfter(1000, { ok: true }); // resolves after 1 second

const failChain = new MockChain(undefined, false).then(console.log);
failChain.root.failAfter(2000, new Error('Timeout!')); // rejects after 2 seconds

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6. Notes & Best Practices

• Only return MockChain from non-async functions to preserve mockability (will be discussed in a dedicated post).
• Use .root.mock() or .root.fail() to control any node in the chain.
• Access intermediate nodes via .parent (previous node) to inspect or mock earlier states.
• Pass autoStart = false to defer execution until .mock() or .fail() is manually called.

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7. Next Steps

• Explore isolating and testing each distributed node using MockChain.
• Combine MockChain with fetch, WebSocket, or EventEmitter mocks for full control of async logic.