TDD/ testing with streams in NodeJS

manpreet Best Answer 2 years ago

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__(
                                                

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