mitmproxy : mitmproxy is your swiss-army knife for debugging, testing, privacy measurements, and penetration testing. It can be used to intercept, inspect, modify...
vegeta : Vegeta is a versatile HTTP load testing tool built out of a need to drill HTTP services with a constant request rate. It can be used both as a command...
Vcr : Record your test suite's HTTP interactions and replay them during future test runs for fast, deterministic, accurate tests.
GoReplay : GoReplay is an open-source tool for capturing and replaying live HTTP traffic into a test environment in order to continuously test your system with r...
httpbin.org : A simple HTTP Request & Response Service.
toxy is a fully programmatic and hackable HTTP proxy to simulate server failure scenarios and unexpected network conditions, built for node.js/io.js.