RxSandbox: RxJS Marble Diagram Test Suite

RxSandbox is a dedicated testing utility for RxJS Observables, employing a Domain Specific Language (DSL) based on marble diagrams to simplify assertions over virtual time. The current stable version, 2.0.5, is designed specifically for RxJS 7.0.1 and newer, while earlier major versions (1.x) supported RxJS 6.x, and pre-1.x versions accommodated RxJS 5. The project is actively maintained, though its development cadence is primarily tied to upstream RxJS releases rather than continuous feature additions, as it's considered feature-complete. It differentiates itself from the core RxJS `TestScheduler` by offering an extended marble diagram DSL, requiring near-zero configuration, operating independently of specific test frameworks, and supporting flexible `TestMessage` creation for granular testing scenarios.