Node.JS Twitter Count Module

I would like someone review this code and tell if it can be done better, or if the code is elegant and simple enough for the task at hand.

I used code climate and I got 4/4 and my test coverage is 96%, yet I would like a professional opinion about it.

'use strict';

var PromisePolyfill = require('promise');
var http = require('http');

var twitterCountURL = 'http://urls.api.twitter.com/1/urls/count.json?url=';

/**
 * Gets the numbers of tweets of a given url.
 * @param {string} validUrl - The url to query
 * @returns {Number} Number of tweets
*/
exports.getCount = function(validUrl) {
    return new PromisePolyfill(function(resolve, reject) {
        if (validUrl) {
            http.get(twitterCountURL + validUrl, function(res) {
                var body = '';
                res.on('data', function(chunk) {
                    body += chunk;
                });
                res.on('end', function() {
                    var twResponse = JSON.parse(body);
                    if (!twResponse.count) {
                        twResponse.count = 0;
                    }
                    // console.log(twResponse.count);
                    resolve(twResponse.count);
                });

            }).on('error', function(e) {
                reject(e.message);
            });

        }else {
            resolve(0);
        }
    });
};

And its respective test file:

'use strict';

var chai = require('chai');
var chaiAsPromised = require('chai-as-promised');
var sinon = require('sinon');
var http = require('http');
var PassThrough = require('stream').PassThrough;
var twitterCount = require('../../modules/twitterCount');

var response,
  responsePT;

chai.should();
chai.use(chaiAsPromised);

describe('twitterCount Module', function() {

    beforeEach(function(done) {
        response = new PassThrough();
        responsePT = new PassThrough();
        sinon.stub(http, 'get');
        done();
    });

    afterEach(function(done) {
        http.get.restore();
        done();
    });

    it('should return valid count when a valid url is passed', function(done) {
        var expected = {'count': 234453234, 'url': 'http:\/\/www.google.com\/'};

        response.write(JSON.stringify(expected));
        response.end();

        http.get.callsArgWith(1, response)
                .returns(responsePT);

        twitterCount.getCount('http://www.google.com').should.eventually.equal(234453234).notify(done);
    });

    it('should return 0 when a invalid url is passed', function(done) {
        var expected = {'count': 0, 'url': 'http:\/\/invalidurl.invalid\/'};

        response.write(JSON.stringify(expected));
        response.end();

        http.get.callsArgWith(1, response)
                .returns(responsePT);

        twitterCount.getCount('http://invalidurl.invalid').should.eventually.equal(0).notify(done);
    });

    it('should return 0 when an empty url is passed', function(done) {
        var expected = {'count': 0, 'url': ''};

        response.write(JSON.stringify(expected));
        response.end();

        http.get.callsArgWith(1, response)
                .returns(responsePT);

        twitterCount.getCount('').should.eventually.equal(0).notify(done);
    });
});