RxJS - Marble Testing

A guide to marble testing in RxJS, starting with an explanation of hot vs cold observables and their producers. Covers the marble syntax characters (frames, time progression, completion, error, sync groupings, subscription points), then walks through practical examples using TestScheduler: testing cold observables with values, testing time-based operators like delay and concatMap, testing hot observables with subscription points, and verifying subscription timing using expectSubscriptions.