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Assertions for use with RxJS and Unexpected

This module is a plugin for the Unexpected assertion library which provides handy assertions against RxJS Observables.


Both rxjs and unexpected are peer dependencies of this module.

$ npm install rxjs@^6 # peer dependency
$ npm install unexpected unexpected-rxjs --save-dev


Use as an Unexpected plugin in Node.js:

const unexpected = require('unexpected');
const expect = unexpected.clone().use(require('unexpected-rxjs'));

Or using ES modules:

import unexpected from 'unexpected';
import unexpectedRxjs from 'unexpected-rxjs';
const expect = unexpected.clone().use(unexpectedRxjs);

Browser, using globals:

const unexpected = window.weknowhow.expect;
const expect = unexpected.clone().use(window.unexpectedRxjs);


import {of} from 'rxjs';

describe('contrived example', function() {
  it('should emit "foo"', function() {
    return expect(of('foo', 'bar'), 'to emit values', 'foo', 'bar');


Note: All assertions return Promise values, so you will want to return expect(/*...*/) (using Mocha) or otherwise use async functions.

  • <Observable> to complete - Asserts an Observable completes. Given the halting problem, this can only fail if the Observable emits an error or your test framework times out.
  • <Observable> [not] to emit (value|values) <any+> - Asserts an Observable emits one or more values using object equivalence.
  • <Observable> [not] to emit times <count> - Asserts an Observable emits count times.
  • <Observable> [not] to emit (once|twice|thrice) - Sugar for previous assertion.
  • <Observable> [not] to emit error <any?> - Asserts an Observable emits an "error"; uses Unexpected's default error matching.
  • <Observable> to emit error [exhaustively] satisfying <any> - Asserts an Observable emits an "error" using "to satisfy" semantics.
  • <Observable> [not] to complete with value <any+> - Assert when an Observable completes, it has emitted one or more matching values.
  • <Observable> [not] to complete with value [exhaustively] satisfying <any+> - Same as previous, except using "to satisfy" semantics.
  • <Observable> when complete <assertion> - Akin to Unexpected's <Promise> when fulfilled <assertion> syntax.


Execute npm run build to bundle the project for distribution.


  • <Observable> [not] to complete with value [exhaustively] satisfying <any+> has some significant performance issues.


Copyright © 2019 IBM. Licensed Apache-2.0