Is  your idea here to have this be global?  If so, why not mimic what would actually happen, and put it on the window (i.e., FakeWindow) object?

```
window.VTTCue === VTTCue; // true
```

I would probably do something like:

```javascript
funciton FakeWindow() {
...
}

FakeWindow.VTTCue = function(startTime, endTime, text) {
...
};

module.exports = FakeWindow;
```

I think it's odd to have to require fake-window and then reach in for the window object vs. just using the module as a whole.