Nock

Getting Started ​

Nock is an HTTP mocking and expectations library for Node.js. It lets you test code that makes HTTP requests without depending on a live service.

Nock uses @mswjs/interceptors to intercept Node.js HTTP requests and fetch.

Install Nock ​

Install Nock as a development dependency with your package manager:

sh
npm install --save-dev nock
# or
pnpm add --save-dev nock
# or
yarn add --dev nock

Create a Mock ​

Define an interceptor before the request. Nock matches the origin and request details, then returns the configured response.

js
import assert from 'node:assert/strict'
import nock from 'nock'

const scope = nock('https://api.github.com')
  .get('/repos/atom/atom/license')
  .reply(200, { license: { key: 'mit', name: 'MIT License' } })

const response = await fetch('https://api.github.com/repos/atom/atom/license')
assert.equal(response.status, 200)
assert.deepEqual(await response.json(), {
  license: { key: 'mit', name: 'MIT License' },
})
scope.done()

Interceptors are consumed

By default, each interceptor is consumed by one matching request. This means you can mock two calls to the same URL with different replies, but you must define one interceptor per expected request. Use persist() when repeated requests should receive the same response, or times() for an exact count.

Core Concepts ​

  • A scope represents a request origin, such as https://api.example.com, and can contain one or more interceptors.
  • An interceptor describes a request method and path, optional matchers, and the reply Nock should return.
  • By default, an interceptor is consumed by its first matching request. Use repeating and optional interceptors to change that behavior.
  • A request that does not match an interceptor on a mocked origin receives a 501 response with code ERR_NOCK_NO_MATCH. Requests to unmocked origins are governed by network controls.