TripMode - Manage your Mac's broadband usage while on a hotspot
Fast.com - Quickly test your internet speed with this fast-loading speed test powered by Netflix.
Slowy app - Simulate custom Internet connection speeds for testing
LibreSpeed - Self-hosted Speedtest for HTML5. Easy setup, examples, configurable, mobile friendly.
Meteor - Meteor is a set of new technologies for building top-quality web apps in a fraction of the time.
speedtest-cli - Test your download speed using SpeedTest on the command-line