function TestFixture() {
        return ((window.Reflect && Reflect.construct) ?
            Reflect.construct(HTMLElement, [], TestFixture)
            : HTMLElement.call(this)) || this;
      }
      TestFixture.prototype = TestFixturePrototype;
      // `constructor` is not writable on Safari 9, but is configurable.
      Object.defineProperty(TestFixture.prototype, 'constructor', {
        configurable: true,
        enumerable: true,
        writable: true,
        value: TestFixture,
      });
      w