nock / nock

HTTP server mocking and expectations library for Node.js

mountebank-testing / mountebank

Over the wire test doubles

jakerella / jquery-mockjax

The jQuery Mockjax Plugin provides a simple and extremely flexible interface for mocking or simulating ajax requests and responses

Kong / insomnia-mockbin

Insomnia Mockbin is the underlying backend for the API mocks capability of Insomnia. It is built and used by Kong, the author of the open-source Kong Gateway.

testdouble / testdouble.js

A minimal test double library for TDD with JavaScript