TDD/ testing with streams in NodeJS

Question

I've been trying to find a reasonable way to test code that uses streams. Has anyone found a reasonable way/ framework to help testing code that uses streams in nodejs?

For example:

var fs = require('fs'),     request = require('request');  module.exports = function (url, path, callback) {   request(url)     .pipe(fs.createWriteStream(path))     .on('finish', function () {       callback();     }); }; 

My current way of testing this type of code either involves simplifying the code with streams so much that I can abstract it out to a non-tested chunk of code or by writing something like this:

var rewire = require('rewire'),     download = rewire('../lib/download'),     stream = require('stream'),     util = require('util');  describe('download', function () {   it('should download a url', function (done) {     var fakeRequest, fakeFs, FakeStream;      FakeStream = function () {       stream.Writable.call(this);     };      util.inherits(FakeStream, stream.Writable);      FakeStream.prototype._write = function (data, encoding, cb) {       expect(data.toString()).toEqual("hello world")       cb();     };      fakeRequest = function (url) {       var output = new stream.Readable();        output.push("hello world");       output.push(null);        expect(url).toEqual('http://hello');        return output;     };      fakeFs = {       createWriteStream: function (path) {         expect(path).toEqual('hello.txt');         return new FakeStream();       }     };      download.__set__('fs', fakeFs);     download.__set__('request', fakeRequest);      download('http://hello', 'hello.txt', function () {       done();     });    }); }); 

Has anyone come up with more elegant ways of testing streams?

Answer 1

Made streamtest for that purpose. It not only make streams tests cleaner but also allows to test V1 and V2 streams https://www.npmjs.com/package/streamtest

Answer 2

I've also been using memorystream, but then putting my assertions into the finish event. That way it looks more like a real use of the stream being tested:

require('chai').should();  var fs = require('fs'); var path = require('path');  var MemoryStream = require('memorystream'); var memStream = MemoryStream.createWriteStream();  /**  * This is the Transform that we want to test:  */  var Parser = require('../lib/parser'); var parser = new Parser();  describe('Parser', function(){   it('something', function(done){     fs.createReadStream(path.join(__dirname, 'something.txt'))       .pipe(parser)       .pipe(memStream)       .on('finish', function() {          /**          * Check that our parser has created the right output:          */          memStream           .toString()           .should.eql('something');         done();       });   }); }); 

Checking objects can be done like this:

var memStream = MemoryStream.createWriteStream(null, {objectMode: true}); . . .       .on('finish', function() {         memStream           .queue[0]           .should.eql({ some: 'thing' });         done();       }); . . .