rxjs-marbles

rxjs-marbles

What is it?

rxjs-marbles is an RxJS marble testing library that should be compatible with any test framework. It wraps the RxJS TestScheduler and provides methods similar to the basic methods used in RxJS's marble tests.

It can be used with AVA, Jasmine, Jest, Mocha or Tape in the browser or in Node and it supports CommonJS and ES module bundlers.

Why might you need it?

I created this package because I wanted to use RxJS marble tests in a number of projects and those projects used different test frameworks.

There are a number of marble testing packages available - including the Mocha-based implementation in RxJS itself - but I wanted something that was simple, didn't involve messing with globals and beforeEach/afterEach functions and was consistent across test frameworks.

If you are looking for something similar, this might suit.

Install

Install the package using NPM:

npm install rxjs-marbles --save-dev

Getting started

If you're just getting started with marble testing, you might be interested in how I wasted some of my time by not carefully reading the manual: RxJS Marble Testing: RTFM.

Usage

With Jasmine and Mocha

Instead of passing your test function directly to it, pass it to the library's marbles function, like this:

import { marbles } from "rxjs-marbles";

describe("rxjs-marbles", () => {

    it("should support marble tests", marbles((m) => {

        const values = { a: 1, b: 2, c: 3, d: 4 };

        const source =  m.hot("--^-a-b-c-|", values);
        const subs =            "^-------!";
        const expected = m.cold("--b-c-d-|", values);

        const destination = source.map((value) => value + 1);
        m.expect(destination).toBeObservable(expected);
        m.expect(source).toHaveSubscriptions(subs);
    }));
});

With Jest

Instead of passing your test function directly to Jest, pass it to the library's marbles function:

import { marbles } from "rxjs-marbles";

test("it should support marble tests", marbles((m) => {

    const values = { a: 1, b: 2, c: 3, d: 4 };

    const source =  m.hot("--^-a-b-c-|", values);
    const subs =            "^-------!";
    const expected = m.cold("--b-c-d-|", values);

    const destination = source.map((value) => value + 1);
    m.expect(destination).toBeObservable(expected);
    m.expect(source).toHaveSubscriptions(subs);
}));

With AVA

Instead of passing your test function directly to AVA, pass it to the library's marbles function. The marbles function will concatenate the additional TestContext argument it receives from AVA.

There is an /ava directory in the package that includes a wrapper that will correctly type additional argument and will call configure - passing AVA's assertion methods to ensure marble assertions will be counted towards AVA's plan - so be sure to specify rxjs-marbles/ava in the import statement or require call:

import { test } from "ava";
import { marbles } from "rxjs-marbles/ava";

test("it should support marble tests", marbles((m, t) => {

    t.plan(2);

    const values = { a: 1, b: 2, c: 3, d: 4 };

    const source =  m.hot("--^-a-b-c-|", values);
    const subs =            "^-------!";
    const expected = m.cold("--b-c-d-|", values);

    const destination = source.map((value) => value + 1);
    m.expect(destination).toBeObservable(expected);
    m.expect(source).toHaveSubscriptions(subs);
}));

With Tape

Instead of passing your test function directly to Tape, pass it to the library's marbles function. The marbles function will concatenate the additional Test argument it receives from Tape.

There is a /tape directory in the package that includes a wrapper that will correctly type additional argument and will call configure - passing Tape's assertion methods to ensure marble assertions will be counted towards Tape's plan - so be sure to specify rxjs-marbles/tape in the import statement or require call:

import * as tape from "tape";
import { marbles } from "rxjs-marbles/tape";

tape("it should support marble tests", marbles((m, t) => {

    t.plan(2);

    const values = { a: 1, b: 2, c: 3, d: 4 };

    const source =  m.hot("--^-a-b-c-|", values);
    const subs =            "^-------!";
    const expected = m.cold("--b-c-d-|", values);

    const destination = source.map((value) => value + 1);
    m.expect(destination).toBeObservable(expected);
    m.expect(source).toHaveSubscriptions(subs);
}));

Alternate assertion methods

If the BDD syntax is something you really don't like, there are some alternative methods on the Context that are more terse:

const source =  m.hot("--^-a-b-c-|", values);
const subs =            "^-------!";
const expected = m.cold("--b-c-d-|", values);

const destination = source.map((value) => value + 1);
m.equal(destination, expected);
m.has(source, subs);

Using cases for test variations

In addition to the marbles function, the library exports a cases function that can be used to reduce test boilerplate by specifying multiple cases for variations of a single test. The API is based on that of jest-in-case, but also includes the marbles context.

The cases implementation is framework-specific, so the import should specify the framework. For example, with Jasmine, you would import cases and use it instead of the it function, like this:

import { cases } from "rxjs-marbles/jasmine";

describe("rxjs-marbles", () => {

    cases("should support cases", (m, c) => {

        const values = { a: 1, b: 2, c: 3, d: 4 };
        const source =  m.hot(c.s, values);
        const expected = m.cold(c.e, values);
        const destination = source.map((value) => value + 1);
        m.expect(destination).toBeObservable(expected);

    }, {
        "non-empty": {
            s: "-a-b-c-|",
            e: "-b-c-d-|"
        },
        "empty": {
            s: "-|",
            e: "-|"
        }
    });
});

With AVA and Tape, the cases function also receives the test context. For example, with AVA, you would import cases and use it instead of the test function, like this:

import { cases } from "rxjs-marbles/ava";

cases("should support cases", (m, c, t) => {

    t.plan(1);

    const values = { a: 1, b: 2, c: 3, d: 4 };
    const source =  m.hot(c.s, values);
    const expected = m.cold(c.e, values);
    const destination = source.map((value) => value + 1);
    m.equal(destination, expected);

}, {
    "non-empty": {
        s: "-a-b-c-|",
        e: "-b-c-d-|"
    },
    "empty": {
        s: "-|",
        e: "-|"
    }
});

Dealing with deeply-nested schedulers

Sometimes, passing the TestScheduler instance to the code under test can be tedious. The context includes a bind method that can be used to bind a scheduler's now and schedule methods to those of the context's TestScheduler.

bind can be passed specific scheduler instances or can be called with no arguments to bind RxJS's animationFrame, asap, async and queue schedulers to the context's TestScheduler.

For example:

it("should support binding non-test schedulers", marbles((m) => {

    m.bind();

    const source =  m.hot("--^-a-b-c-|");
    const subs =            "^--------!";
    const expected =        "---a-b-c-|";

    // Note that delay is not passed a scheduler:
    const destination = source.delay(m.time("-|"));
    m.expect(destination).toBeObservable(expected);
    m.expect(source).toHaveSubscriptions(subs);
}));

API

The rxjs-marbles API is comprised of two functions:

• configure
• marbles

configure

interface Configuration {
    assert?: (value: any, message: string) => void;
    assertDeepEqual?: (a: any, b: any) => void;
    frameworkMatcher?: boolean;
}

function configure(options: Configuration): void;

The configure method can be used to specify the assertion functions that are to be used. Calling it is optional; it's only necessary if particular assertion functions are to be used.

The default implementations simply perform the assertion and throw an error for failed assertions.

marbles

function marbles(test: (context: Context) => any): () => any;
function marbles<T1>(test: (context: Context, t1: T1) => any): (t1: T1) => any;
function marbles<T1, T2>(test: (context: Context, t1: T1, t2: T2) => any): (t1: T1, t2: T2) => any;
function marbles<T1, T2, T3>(test: (context: Context, t1: T1, t2: T2, t3: T3) => any): (t1: T1, t2: T2, t3: T3) => any;

marbles is passed the test function, which it wraps, passing the wrapper to the test framework. When the test function is called, it is passed the Context - which contains methods that correspond to the basic methods described in the RxJS documentation:

interface Context {
    autoFlush: boolean;
    bind(...schedulers: IScheduler[]): void;
    cold<T = any>(marbles: string, values?: any, error?: any): ColdObservable<T>;
    configure(options: Configuration): void;
    equal<T = any>(actual: Observable<T>, expected: Observable<T>): void;
    equal<T = any>(actual: Observable<T>, expected: string, values?: { [key: string]: T }, error?: any): void;
    equal<T = any>(actual: Observable<T>, unsubscription: string, expected: Observable<T>): void;
    equal<T = any>(actual: Observable<T>, unsubscription: string, expected: string, values?: { [key: string]: T }, error?: any): void;
    expect<T = any>(actual: Observable<T>, unsubscription?: string): Expect<T>;
    flush(): void;
    has<T = any>(actual: Observable<T>, expected: string | string[]): void;
    hot<T = any>(marbles: string, values?: any, error?: any): HotObservable<T>;
    readonly scheduler: TestScheduler;
    teardown(): void;
    time(marbles: string): number;
}

interface Expect<T> {
    toBeObservable(expected: ColdObservable<T> | HotObservable<T>): void;
    toBeObservable(expected: string, values?: { [key: string]: T }, error?: any): void;
    toHaveSubscriptions(expected: string | string[]): void;
}