If when you run your tests you see an error similar to this
Failed to execute ‘send’ on ‘XMLHttpRequest’: Failed to load ‘ng:///DynamicTestModule/xxxxxxComponent_Host.ngfactory.js
It means something in your component is throwing an exception and the test framework is returning a wrapped exception. To see the actual exception run ng test with -sm=false as a parameter
ng test -sm=false
This will not only stop your browser from freezing on that test, but will also give you the original error including line number.