Testing asynchronous function with mocha

I want to test a asynchronous javascript function that runs in node.js and makes a simple request to a http api:

const HOST = 'localhost';
const PORT = 80;

http = require('http');

var options = {
    host: HOST,
    port: PORT,
    path: '/api/getUser/?userCookieId=26cf7a34c0b91335fbb701f35d118c4c32566bce',
    method: 'GET'
};
doRequest(options, myCallback);

function doRequest(options, callback) {

    var protocol = options.port == 443 ? https : http;
    var req = protocol.request(options, function(res) {

        var output = '';
        res.setEncoding('utf8');

        res.on('data', function(chunk) {
            console.log(chunk);
            output += chunk;
        });

        res.on('error', function(err) {
            throw err;
        });

        res.on('end', function() {
            var dataRes = JSON.parse(output);
            if(res.statusCode != 200) {
                throw new Error('error: ' + res.statusCode);
            } else {
                try {
                    callback(dataRes);                        
                } catch(err) {
                    throw err;
                }
            }
        });

    });

    req.on('error', function(err) {
        throw err;
    });

    req.end();

}

function myCallback(dataRes) {
    console.log(dataRes);
}

Executed this code works and the response will be displayed as expected.

If I execute this in a mocha test the request is not executed:

describe('api', function() {
    it('should load a user', function() {
        assert.doesNotThrow(function() {
            doRequest(options, myCallback, function(err) {
                if (err) throw err;
                done();
            });
        });
        assert.equal(res, '{Object ... }');
    });
});

The Problem is, that no code after:

var req = protocol.request(options, function(res) {

is executed not even a simple cons