Error: Module name "phantom" has not been loaded yet for context: _. Use require([])

I'm trying to run a phantom.js test using karma and grunt and I get:

PhantomJS 2.1.1 (Mac OS X 0.0.0) ERROR Error: Module name "webpage" has not been loaded yet for context: _. Use require([]) http://requirejs.org/docs/errors.html#notloaded at vendor/bower/requirejs/require.js:140

The karma config from the Gruntfile.js looks like this:

karma: {
        options: {
            basePath: "./",
            singleRun: true,
            captureTimeout: 7000,
            autoWatch: true,

            reporters: karmaOptions.reporters,
            browsers: ["PhantomJS", "PhantomJS_custom"],

            // you can define custom flags
            customLaunchers: {
                'PhantomJS_custom': {
                    base: 'PhantomJS',
                    options: {
                        windowName: 'my-window',
                        settings: {
                            webSecurityEnabled: false
                        },
                    },
                    flags: ['--load-images=true'],
                    debug: true
                }
            },

            phantomjsLauncher: {
                // Have phantomjs exit if a ResourceError is encountered (useful if karma exits without killing phantom)
                exitOnResourceError: true
            },
files: [ "node_modules/karma-jasmine-async/src/jasmine.async.js", "vendor/bower/requirejs/require.js", "vendor/bower/underscore/underscore.js", "node_modules/phantomjs-prebuilt/bin/phantom.js", "test/runner.js",

                {
                    pattern: "<%= rootFolderName %>/**/*.*",
                    included: false
                },
                {
                    pattern: "test/specs/*.*",
                    included: false
                },
                {
                    pattern: "test/mocks/*.*",
                    included: false
                },
                {
                    pattern: "vendor/**/*.js",
                    included: false
                },
                {
                    pattern: "vendor/**/*.html",
                    included: false
                },
                {
                    pattern: "vendor/**/*.xml",
                    included: false
                }
            ],
            exclude: [
                'dist/**',
                'vendor/**/*Spec.js'
            ]
        },

        // This creates a server that will automatically run your tests when you
        // save a file and display results in the terminal.
        daemon: {
            options: {
                singleRun: false
            }
        },

        // This is useful for running the tests just once.
        run: {
            options: {
                singleRun: true
            }
        },

        run_functional: {
            options: {
                windowName: 'my-window',
                settings: {
                    webSecurityEnabled: false
                }
            }
        }

[...]

grunt.registerTask("test", ["karma:run_functional"]);

The test.js looks like this:

console.log("starting");
var webPage = require('webpage');
var page = webPage.create();
page.windowName = 'my-window';
page.settings.webSecurityEnabled = false;
page.open('http://google.com', function(status) {
    console.log("Status: " + status);
    if(status === "success") {
        debugger;
        console.log("success");
    }
    phantom.exit();
});

Config.js file for configuring require.js looks like this:

require.config({
paths: {
    "vendor": "vendor",
    "node_modules": "node_modules",
    "almond": "node_modules/almond/almond",
    "underscore": "node_modules/lodash/dist/lodash.underscore",
    "jquery": "node_modules/jquery/jquery",
    "jquery-ui": "node_modules/jquery-ui-dist/jquery-ui",
    "backbone": "node_modules/backbone/backbone",
    "layoutmanager": "node_modules/layoutmanager/backbone.layoutmanager",
    "backbone.subroute": "node_modules/backbone.subroute/backbone.subroute",
    "bootstrap": "node_modules/bootstrap/dist/js/bootstrap",
    "i18next": "node_modules/i18next-client/i18next.amd",
    "text": "node_modules/requirejs-text/text",[...]

When I run grunt test from the command line I get the error above:

Error: Module name "webpage" has not been loaded yet for context: _. Use require([])

So the problem is that this webpage module that is part of phantom.js was not loaded by require.js. in test.js Where should I load it? in config.js? should I load the entire phantom.js or just this webpage module?

I did a refactor and my test.js is like this now:

var phantom = require('phantom');

phantom.create(function(ph){
    ph.createPage(function(page) {
        page.windowName = 'my-window';
        page.settings.webSecurityEnabled = false;
        page.open("http://www.google.com", function(status) {
            page.render("google.pdf", function(){
                console.log("page rendered");
                ph.exit();
            })
        })
    })
});

And now I get:

PhantomJS 2.1.1 (Mac OS X 0.0.0) ERROR Error: Module name "phantom" has not been loaded yet for context: _. Use >require([])

Require js should pick it up from config.js to which I appended:

"phantom": "node_modules/phantomjs-prebuilt/bin/phantom.js"

But for some reason require js doesn't see include phantom js. Why is that happening.