fetch-mock

Features include:

mocks most of the fetch API spec, even advanced behaviours such as streaming and aborting
declarative matching for most aspects of a http request, including url, headers, body and query parameters
shorthands for the most commonly used features, such as matching a http method or matching one fetch only
support for delaying responses, or using your own async functions to define custom race conditions
can be used as a spy to observe real network requests
can be extended with your own reusable custom matchers that can be used both for matching fetch-calls and inspecting the results
isomorphic, and supports either a global fetch instance or a locally required instance

Requirements

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

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)