Mockttp vs Pretender.js

Mockttp is a free, open-source JavaScript library for intercepting, transforming, or testing HTTP requests and responses. It supports integration tests in Node.js and browsers, including transparent proxying and HTTPS. Its tools can stub responses, verify requests, generate self-signed certificates for HTTPS mocking, and mock traffic inside or outside the process. It can also serve as the basis for custom proxies that capture, inspect, or rewrite traffic. For parallel tests, Mockttp can automatically configure ports, mock URLs, and proxy settings. It works with promise-capable testing tools and HTTP clients; Mocha, Chai, and Superagent appear in an example but are optional. Browser tests require an admin server running outside the browser. The setup guide warns against trusting a test certificate authority system-wide or sharing its private key, because either could allow an attacker to impersonate secure connections. Mockttp supports Linux, macOS, Windows, web, and self-hosted use.

Pretender.js has no write-up on Specifiction yet; its figures are above.