jasmine unit test for javascript CustomEvent

How do I test that a CustomEvent is dispatched in jasmine? When I try running the following code I get the error: "ReferenceError: Can't find variable: CustomEvent".

function testCustomEvent() {
  window.dispatchEvent(new CustomEvent('myCustomEvent', {
    detail: 'foo'
  }));
}

describe('testCustomEvent', function() {
  it('dispatches myCustomEvent', function() {
    var eventSpy = jasmine.createSpy();
    window.addEventListener('myCustomEvent', eventSpy);

    testCustomEvent();

    expect(eventSpy).toHaveBeenCalledWith('foo');
  });
});