@rxjs/test

Implementation-neutral virtual-time and marble testing for RxJS 9 Observable contracts.

npm install --save-dev @rxjs/test@next rxjs@next

import 'rxjs';
import { rxTest } from '@rxjs/test';
import { map } from 'rxjs/map';

await rxTest(({ cold, expectObservable }) => {
  const source = cold('-a-b-|', { a: 1, b: 2 });
  expectObservable(source[map]((value) => value * 10)).toBe('-a-b-|', {
    a: 10,
    b: 20,
  });
});

Use cold() only when the test deliberately needs one producer per direct subscription. Use observable() when the contract should exercise the active platform Observable constructor. The package never installs a platform Observable for the consumer; import rxjs or @rxjs/observable-polyfill first when the realm does not already provide one.

rxTest supplies scheduled work, hot/cold/platform sources, Observable and subscription expectations, explicit time plans, and configurable deep-equality assertions. Failures use RxTestAssertionError and include structured assertion information.

The package requires Node 22.13+, publishes ESM only, and declares an exact peer on the matching RxJS 9 prerelease train. The rxjs migration guide explains how to review lifecycle choices when translating RxJS 7 TestScheduler.run tests.