Module Export callback function returns undefined

Hello: i am new to nodejs and mocha. I trying to use module.exports to return a value from a callback function. However, its returning undefined. For simple cases it works though. Please help.

Result

  Module Export Example
    √ Test Case 1: Module
      Hello Node World!!! (*** this works - its a direct return ***)

    √ Test Case 2: Module
      undefined           (*** this fails - its from  a callback fn ***)

google.js

var requirejs = require('requirejs');       
requirejs.config({ baseUrl: '.', paths: {   }, nodeRequire: require });
describe('Module Export Example', function(){
    var mod;
    before(function(done){
        requirejs(['./googleModule'], 
            function(_mod) {
                mod = _mod;  
                done();
            });
    });  

    it('Test Case 1: Module', function(done){
        console.log(mod.get(done));
    });

    it('Test Case 2: Module', function(done){
        console.log(mod.google(done));
    });

});

googleModule.js

var request = require('request');
module.exports = {
    get: function(done){        
        var a = "Hello Node World!!!";
        return(done(), a);
    },   
    google: function(done){        
        var a = doCallback(function(){
            var b = "PRINT DATA: " + data.statusCode + ' ' + data.headers['content-type'];      
            return(done(), b);
        });
        return(done(), a);
    }
}       

function doCallback(callback, done){
    var options = {url: 'http://www.google.com', headers: {'Content-Type': 'text/html'}, encoding: null};
    request.get(options, function(err, res, body){
        var a  = callback(res, done);
        return (callback(), a); //???????
    });
}

via Bipo K