title: angular 4 unit testing error `TypeError: ctor is not a constructor`
body: <p>I am trying to test my route resolver and while testing I got <code>TypeError: ctor is not a constructor</code> and no idea why it happen while typescript compile time no error.</p>
  
  <pre><code>TypeError: ctor is not a constructor
  TypeError: ctor is not a constructor
      at _createClass (http://localhost:9877/_karma_webpack_/vendor.bundle.js:42355:26)
      at _createProviderInstance$1 (http://localhost:9877/_karma_webpack_/vendor.bundle.js:42330:26)
      at resolveNgModuleDep (http://localhost:9877/_karma_webpack_/vendor.bundle.js:42315:17)
      at _createClass (http://localhost:9877/_karma_webpack_/vendor.bundle.js:42362:26)
      at _createProviderInstance$1 (http://localhost:9877/_karma_webpack_/vendor.bundle.js:42330:26)
      at resolveNgModuleDep (http://localhost:9877/_karma_webpack_/vendor.bundle.js:42315:17)
      at NgModuleRef_.webpackJsonp../node_modules/@angular/core/@angular/core.es5.js.NgModuleRef_.get (http://localhost:9877/_karma_webpack_/vendor.bundle.js:43401:16)
      at TestBed.webpackJsonp../node_modules/@angular/core/@angular/core/testing.es5.js.TestBed.get (http://localhost:9877/_karma_webpack_/vendor.bundle.js:48412:47)
      at http://localhost:9877/_karma_webpack_/vendor.bundle.js:48418:61
      at Array.map (native)
  </code></pre>