@fetch-mock/jest

@fetch-mock/jest

A wrapper for fetch-mock that improves the developer experience when working with jest. It provides the following:

• Adds methods to fetchMock which wrap its default methods, but align more closely with jest's naming conventions.
• Extends expect with convenience methods allowing for expressive tests such as expect(fetchMock).toHavePosted('http://example.com', {id: 'test-id'}).
• Can optionally be hooked in to jest's global mock management methods such as clearAllMocks().

Requirements

@fetch-mock/jest requires either of the following to run:

• jest
• The fetch API, via one of the following:
  • Node.js 18+ for full feature operation
  • Any modern browser that supports the fetch API
  • node-fetch when testing in earlier versions of Node.js (this is untested, but should mostly work)

Installation

npm i -D @fetch-mock/jest

Setup

import fetchMock, { manageFetchMockGlobally } from '@fetch-mock/jest';
import { jest } from '@jest/glonals';

manageFetchMockGlobally(jest); // optional

API

fetchMock

An instance of @fetch-mock/core, with the following methods added:

fetchMock.mockClear()

Clears all call history from the mocked fetch implementation.

fetchMock.mockReset({includeSticky: boolean})

Clears all call history from the mocked fetch implementation and removes all routes (including fallback routes defined using .spy() or .catch()) with the exception of sticky routes. To remove these, pass in the includeSticky: true option. FOr more fine grained control over fallback routes and named routes please use fetchMock.removeRoutes()

fetchMock.mockRestore({includeSticky: boolean})

Calls mockReset() and additionally restores global fetch to its unmocked implementation.

manageFetchMockGlobally(jest)

Hooks fetchMock up to jest's global mock management so that

• jest.clearAllMocks() will call fetchMock.mockClear()
• jest.resetAllMocks() will call fetchMock.mockReset()
• jest.restoreAllMocks() will call fetchMock.mockRestore()

Note that these will not clear any sticky routes added to fetchMock. You will need to make an additional call to fetchMock.removeRoutes({includeSticky: true}).

Expect extensions

These are added to jest automatically and are available on any expect call that is passed fetchMock as an argument. Their behaviour is similar to the jest expectation methods mentioned in the comments below

expect(fetchMock).toHaveFetched(filter, options); // .toHaveBeenCalled()/.toHaveBeenCalledWith()
expect(fetchMock).toHaveLastFetched(filter, options); // .toHaveBeenLastCalledWith()
expect(fetchMock).toHaveNthFetched(n, filter, options); //  .toHaveBeenNthCalled()/.toHaveBeenNthCalledWith()
expect(fetchMock).toHaveFetchedTimes(n, filter, options); // .toHaveBeenCalledTimes()
expect(fetchMock).toBeDone(filter);

Notes

• filter and options are the same as those used by fetchMock.callHistory.calls().
• Each method can be prefixed with the .not helper for negative assertions. e.g. expect(fetchMock).not.toBeDone('my-route')
• In each of the method names Fetched can be replaced by any of the following verbs to scope to a particular method:
  • Got
  • Posted
  • Put
  • Deleted
  • FetchedHead
  • Patched e.g. expect(fetchMock).toHaveDeleted('http://example.com/user/1')