Angular 2 testing karma with webpack Can't find variable: Map

I am trying to test my directive with karma and webpack. This is the karma config file

module.exports = function (config) {
    config.set({
        basePath: './',
        frameworks: ["jasmine"],
        files: [
            {
            pattern: 'directive.spec.ts',
            watched: false
        }],
        exclude: [],
        preprocessors: {
            'directive.spec.ts': ['webpack', 'sourcemap']
        },
        webpackServer: {
            noInfo: true
        },
        port: 9876,
        colors: true,
        logLevel: config.LOG_INFO,
        autoWatch: false,
        browsers: [
            "PhantomJS"
        ],
        singleRun: true,
        reporters: ['mocha'],
        webpack: {
            resolve: {
                extensions: ['', '.ts', '.js'],
                modulesDirectories: ['node_modules', '.'],
            },
            module: {
                loaders: [{
                    test: /\.ts$/,
                    loader: 'awesome-typescript-loader'
                }]
            },
            stats: {
                colors: true,
                reasons: true
            },
            debug: true,
            devtool: 'inline-source-map'
        }
    });
};

And the directive.spec.ts:

import { MyDirective } from './directive';
import {TestComponent} from './test';
import {
  async,
  inject,
  TestBed,
} from '@angular/core/testing';

describe('TestComponent', () => {

  let fixture: any;

beforeEach(() => {
  fixture = TestBed.configureTestingModule({
    declarations: [ TestComponent, MyDirective]
  })
  .createComponent(TestComponent);
  fixture.detectChanges();
});

  it('should work', () => {
    expect(true).toBe(true);
  });

But when I am trying to run my test I am getting this error:

PhantomJS 2.1.1 (Mac OS X 0.0.0) ERROR ReferenceError: Can't find variable: Map at directive.spec.ts:1380

What am I missing here?