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rx-sandbox

Marble diagram DSL based test suite for RxJS 6

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RxSandbox

RxSandbox is test suite for RxJS, based on marble diagram DSL for easier assertion around Observables. For RxJS 5 support, check pre-1.x versions. 1.x supports latest RxJS 6.x. 2.* is available to support rxjs@7.0.1 and above.

What's difference with TestScheduler in RxJS?

RxJs core itself includes its own TestScheduler implementation. With latest updates, it have different semantics around how to translate virtual frame and time progression also slightly different api surfaces based on callbacks. RxSandbox aims to provide test interface with below design goals, bit different to core's test scheduler.

  • Support extended marble diagram DSL
  • Near-zero configuration, works out of box
  • No dependencies to specific test framework
  • Flexible TestMessage support: test can be created from marble syntax, but also can be created from plain objects.

Install

This has a peer dependencies of rxjs@6.*.*, which will have to be installed as well.

npm install rx-sandbox

Usage

Observable marble diagram token description

In RxSandbox, Observable is represented via marble diagram. Marble syntax is a string represents events happening over virtual time so called as frame.

  • - : Single frame of time passage, by default 1.
  • | : Successful completion of an observable signaling complete().
  • # : An error terminating the observable signaling error().
  • (whitespace) : Noop, whitespace does nothing but allows align marbles for readability.
  • a : Any other character than predefined token represents a value being emitted by next()
  • () : When multiple events need to single in the same frame synchronously, parenthesis are used to group those events. You can group nexted values, a completion or an error in this manner. The position of the initial (determines the time at which its values are emitted.
  • ^ : (hot observables only) Shows the point at which the tested observables will be subscribed to the hot observable. This is the "zero frame" for that observable, every frame before the ^ will be negative.
  • ! : (for subscription testing) Shows the point at which the tested observables will be unsubscribed.
  • ...n... : (n is number) Expanding timeframe. For cases of testing long time period in observable, can shorten marble diagram instead of repeating -.

The first character of marble string always represents 0 frame.

Few examples

const never = `------`; // Observable.never() regardless of number of `-`
const empty = `|`;      // Observable.empty();
const error = `#`;      // Observable.throw(`#`);
const obs1 = `----a----`;
//`           01234    `, emits `a` on frame 4
const obs2 = `----a---|`;
//`           012345678`, emits `a` on frame 4, completes on 8
const obs2 = `-a-^-b--|`;
//`              012345`, emits `b` on frame 2, completes on 5 - hot observable only
const obs3 = `--(abc)-|`;
//`           012222234, emits `a`,`b`,`c` on frame 2, completes on 4
const obs4 = `----(a|)`;
//`           01234444, emits `a` and complets on frame 4
const obs5 = ` - --a- -|`;
//`            0 1234 56, emits `a` on frame 3, completes on frame 6
const obs6 = `--...4...--|`
//`           01......5678, completes on 8

Subscription marble diagram token description

The subscription marble syntax is slightly different to conventional marble syntax. It represents the subscription and an unsubscription points happening over time. There should be no other type of event represented in such diagram.

  • - : Single frame of time passage, by default 1.
  • ^ : Shows the point in time at which a subscription happen.
  • ! : Shows the point in time at which a subscription is unsubscribed.
  • (whitespace) : Noop, whitespace does nothing but allows align marbles for readability.
  • ...n... : (n is number) Expanding timeframe. For cases of testing long time period in observable, can shorten marble diagram instead of repeating -.

There should be at most one ^ point in a subscription marble diagram, and at most one ! point. Other than that, the - character is the only one allowed in a subscription marble diagram.

Few examples

const sub1 = `-----`; // no subscription
const sub2 = `--^--`;
//`           012`, subscription happend on frame 2, not unsubscribed
const sub3 = `--^--!-`;
//`           012345, subscription happend on frame 2, unsubscribed on frame 5

Anatomy of test interface

You can import rxSandbox, and create instance using create().

import { expect } from 'chai';
import { rxSandbox } from 'rx-sandbox';

it('testcase', () => {
  const { hot, cold, flush, getMessages, e, s } = rxSandbox.create();
  const e1 = hot('  --^--a--b--|');
  const e2 = cold('   ---x--y--|', {x: 1, y: 2});

  const expected = e('       ---q--r--|');
  const sub =      s('       ^        !');

  const messages = getMessages(e1.merge(e2));

  flush();

  //assertion
  expect(messages).to.deep.equal(expected);
  expect(e1.subscriptions).to.deep.equal(sub);
});

Creating sandbox

rxSandbox.create(autoFlush?: boolean, frameTimeFactor?: number, maxFrameValue?: number): RxSandboxInstance

rxSandbox.create({
  autoFlush?: boolean,
  frameTimeFactor?: number,
  maxFrameValue?: boolean,
  flushWithAsyncTick?: boolean,
}): RxSandboxInstance | RxAsyncSandboxInstance

frameTimeFactor allows to override default frame passage 1 to given value. maxFrameValue allows to override maximum frame number testscheduler will accept. (1000 by default). Maxframevalue is relavant to frameTimeFactor. (i.e if frameTimeFactor = 2 and maxFrameValue = 4, -- will represent max frame)

Refer below for autoFlush option.

Using RxSandboxInstance

RxSandboxInstance exposes below interfaces.

Creating hot, cold observable

hot<T = string>(marble: string, value?: { [key: string]: T } | null, error?: any): HotObservable<T>;
hot<T = string>(messages: Array<TestMessage<T>>): HotObservable<T>;

cold<T = string>(marble: string, value?: { [key: string]: T } | null, error?: any): ColdObservable<T>;
cold<T = string>(messages: Array<TestMessage<T>>): ColdObservable<T>;

Both interfaces accepts marble diagram string, and optionally accepts custom values for marble values or errors. Otherwise, you can create Array<TestMessage<T>> directly instead of marble diagram.

Creating expected value, subscriptions

To compare observable's result, we can use marble diagram as well wrapped by utility function to generate values to be asserted.

e<T = string>(marble: string, value?: { [key: string]: T } | null, error?: any): Array<TestMessage<T>>;

//const expected = e(`----a---b--|`);

It accepts same parameter to hot / cold observable creation but instead of returning observable, returns array of metadata for marble diagram.

Subscription metadata also need to be generated via wrapped function.

s(marble: string): SubscriptionLog;

//const subs = s('--^---!');

Getting values from observable

Once we have hot, cold observables we can get metadata from those observables as well to assert with expected metadata values.

getMessages<T = string>(observable: Observable<any>, unsubscriptionMarbls: string = null): Array<TestMessage<T>>>;

const e1 = hot('--a--b--|');
const messages = getMessages(e1.mapTo('x'));

//at this moment, messages are empty!
assert(messages.length === 0);

It is important to note at the moment of getting metadata array, it is not filled with actual value but just empty array. Scheduler should be flushed to fill in values.

const e1 = hot('    --a--b--|');
const expected = e('--x--x--|')
const subs = s(`    ^       !`);
const messages = getMessages(e1.mapTo('x'));

//at this moment, messages are empty!
expect(messages).to.be.empty;

flush();

//now values are available
expect(messages).to.deep.equal(expected);
//subscriptions are also available too
expect(e1.subscriptions).to.deep.equal(subs);

Or if you need to control timeframe instead of flush out whole at once, you can use advanceTo as well.

const e1 = hot('    --a--b--|');
const subs = s(`    ^       !`);
const messages = getMessages(e1.mapTo('x'));

//at this moment, messages are empty!
expect(messages).to.be.empty;

advanceTo(3);
const expected = e('--x------'); // we're flushing to frame 3 only, so rest of marbles are not constructed

//now values are available
expect(messages).to.deep.equal(expected);
//subscriptions are also available too
expect(e1.subscriptions).to.deep.equal(subs);

Flushing scheduler automatically

By default sandbox instance requires to flush() explicitly to execute observables. For cases each test case doesn't require to schedule multiple observables but only need to test single, we can create sandbox instance to flush automatically. Since it flushes scheduler as soon as getMessages being called, subsequent getMessages call will raise errors.

const { hot, e } = rxSandbox.create(true);

const e1 = hot('    --a--b--|');
const expected = e('--x--x--|')
const messages = getMessages(e1.mapTo('x'));

//without flushing, observable immeditealy executes and values are available.
expect(messages).to.deep.equal(expected);

//subsequent attempt will throw
expect(() => getMessages(e1.mapTo('y'))).to.throw();

Scheduling flush into native async tick (Experimental, 2.0 only)

If you create sandbox instance with flushWithAsyncTick option, sandbox will return instance of RxAsyncSandboxInstance which all of flush interfaces need to be asynchronously awaited:

interface RxAsyncSandboxInstance {
  ...,
  advanceTo(toFrame: number) => Promise<void>;
  flush: () => Promise<void>;
  getMessages: <T = string>(observable: Observable<T>, unsubscriptionMarbles?: string | null) => Promise<void>;
}

It is not uncommon practices chaining native async function or promise inside of observables, especially for inner observables. Let's say if there's a redux-observable epic like below

const epic = (actionObservable) => actionObservable.ofType(...).pipe((mergeMap) => {
  return new Promise.resolve(...);
})

Testing this epic via rxSandbox won't work. Once sandbox flush all internal actions synchronously, promises are still scheduled into next tick so there's no inner observable subscription value collected by flush. RxAsyncSandboxInstance in opposite no longer flush actions synchronously but schedule each individual action into promise tick to try to collect values from async functions.

NOTE: this is beta feature and likely have some issues. Also until stablized internal implementation can change without semver breaking.

Custom frame time factor

Each timeframe - is predefined to 1, can be overridden.

const { e } = rxSandbox.create(false, 10);

const expected = e('--x--x--|');

// now each frame takes 10
expect(expected[0].frame).to.equal(20);

Custom assertion for marble diagram

Messages generated by rxSandbox is plain object array, so any kind of assertion can be used. In addition to those, rxSandbox provides own custom assertion method marbleAssert for easier marble diagram diff.

marbleAssert<T = string>(source: Array<SubscriptionLog | TestMessage<T>>): { to: { equal(expected: Array<SubscriptionLog | TestMessage<T>>): void } }

It accepts array of test messages generated by getMessages and e, or subscription log by Hot/ColdObservable.subscriptions or s (in case of utility method s it returns single subscription, so need to be constructed as array).

import { rxSandbox } from 'rx-sandbox';
const { marbleAssert } = rxSandbox;

const {hot, e, s, getMessages, flush} = rxSandbox.create();

const source = hot('---a--b--|');
const expected = e('---x--x---|');
const sub = s('^-----!');

const messages = getMessages(source.mapTo('x'));
flush();

marbleAssert(messages).to.equal(expected);
marbleAssert(messages).toEqual(expected); // if you prefer jasmin / jest style matcher syntax
marbleAssert(source.subscriptions).to.equal([sub]);

When assertion fails, it'll display visual / object diff with raw object values for easier debugging.

Assert Observable marble diagram

Assert subscription log marble diagram

Building / Testing

Few npm scripts are supported for build / test code.

  • build: Transpiles code to ES5 commonjs to dist.
  • build:clean: Clean up existing build
  • test: Run unit test. Does not require build before execute test.
  • lint: Run lint over all codebases
  • lint:staged: Run lint only for staged changes. This'll be executed automatically with precommit hook.
  • commit: Commit wizard to write commit message

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