testing streams with chai
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README.md

ExpectStream

Testing streams sucks. So we built this extension to chai to reduce the suck-factor of testing node streams. Now, let's forget about all the drama and call it a victory:

victory

API

As this module extends chai most of the documentation can be found at their website. ExpectStream extends it with new methods for asserting streams asynchronously:

.produce

This method takes either one or multiple values, which are expected to be the only outputs produced by the stream under test or a function that takes the value and checks if it is the expected one. In the latter case, there are three values your callback should return to signal its state:

  • If the function returns 0, the input value is not the expected value, but does not represent an error case either. The test will go on (or timeout).

  • If the function returns 1, it's the signal that the correct value has finally arrived. The assertion will notify the test, that it is successful.

  • If the function returns -1, it signals that the given input value is erroneous. We will be notified of the error via notify.

.eventually

This property allows ExpectStream to ignore mismatches until the correct values are produced.

.exactly

Using this chainable method will adjust the assertion configuration to strict equality. Otherwise ExpectStream validates, if the produced output contains the expected value.

.filter

This method accepts a function, that can be used to ignore some outputs, which is signalled by returning false in this callback.

.on

This method takes the values the stream under test should use to produce its output, if it isn't only a readable stream.

.notify

This method is used to notify the testrunner if an error occurs or if the streams ended and have produced the expected message

.tap

With this method you can tap into the stream under test and inspect whats going on, if an error happens

Usage

Suppose we have a transform stream, that adds a Mr. to the start of every value, that enters it:

// src/Misterizer
import { Transform } from "stream";

export default class Misterizer extends Transform {
	_transform(name, enc, cb) {
		this.push(`Mr. ${name}`);
		cb();
	}
}

Now we'd like to test it, using mocha with ExpectStream:

// src/__tests__/MisterizerTest
import { expect } from "core-assert";
import Misterizer from "../Misterizer"

describe("MisterizerTest", function() {
	// this test passes
	it("Misterizes Circle", function(done) {
		expect(new Misterizer())
			.to.exactly.produce("Mr. Circle")
			.on("Circle")
			.notify(done);
	});

	// this test will trigger a timeout
	it("Misterizes Square", function(done) {
		expect(new Misterizer())
			.to.eventually.produce("Mr. Circle")
			.on("Square")
			.tap(::console.log) // will print "Square, 0)"
			.notify(done);
	});
});

But the mighty power of ExpectStream offers much more functionality, which will be presented by FunnyBot:

// src/FunnyBot
import { Readable } from "stream";

export default class FunnyBot extends Readable {
	constructor(jokes) {
		super({ objectMode: true });
		
		this.jokes = jokes;
	}
	
	_read() {
		return this.push(this.jokes.shift());
	}
}

All that is missing now are some funny jokes:

// src/__tests__/FunnyBotTest
import { expect } from "@circle/core-assert";
import FunnyBot from "../FunnyBot";

describe("FunnyBot", function() {
	it("tells multiple really funny jokes", function() {
		expect(new FunnyBot([{
			date: Date.now(),
			joke: "Hello, I am FunnyBot!"
		}, {
			date: Date.now(),
			joke: "I am not a joke"
		}, {
			date: Date.now(),
			joke: "What do you see when the Pillsbury Dough Boy bends over? Dough nuts"
		}]).filter(x => x.joke !== "I am not a joke").to.produce([{
			joke: "Hello, I am FunnyBot!" 
		}, {
			joke: "What do you see when the Pillsbury Dough Boy bends over? Dough nuts"
		}]).notify(done);
	});
	
	it("thinks about complex problems", function() {
		expect(new FunnyBot([{
			date: Date.now(),
			joke: "Hello, I am FunnyBot!"
		}, {
			date: Date.now(),
			joke: "I am not a joke"
		}, {
			date: Date.now(),
			joke: "The line is an imaginary invention of imperfect biological life forms."
		}]).to.eventually.produce([{
			joke: "Hello, I am FunnyBot!" 
		}, {
			joke: "The line is an imaginary invention of imperfect biological life forms."
		}]).notify(done);
	});
	
	it("writes up some new material", function() {
		expect(new FunnyBot([{
			firstTry: "Error. Error. Banal."
		}, {
			secondTry: "That has been done before."
		}, {
			lastTry: "Funnybot is now finished with final joke."
		}]).to.produce.exactly([{
			firstTry: "Error. Error. Banal."
		}, {
			secondTry: "That has been done before."
		}, {
			lastTry: "Funnybot is now finished with final joke."
		}]).notify(done);	
	});
});

Testing

ExpectStream is tested with mocha by executing make test in the root directory of the project.

Contributing

If you want to contribute to this repository, please ensure ...

  • to use make for development (it validates the source code and transpiles it to /lib).
  • to follow the existing coding style.
  • to use the linting tools that are listed in the package.json (which you get for free when using make).
  • to add and/or customize unit tests for any changed code.
  • to reference the corresponding issue in your pull request with a small description of your changes.

All contributors are listed in the AUTHORS file, sorted by the time of their first contribution.