Can you change this to check against their documented API? Just because we've had the undocumented stuff bite us a couple of times.

Something like:
```
var stub = window.amplitude.logEvent;

// after library loads, inside loop.
expect(window.amplitude.logEvent).not.to.eql(stub);
```

It's true that they could instead always queue and then change the library to read on an interval, but I think it's less likely than changing the name of an internal call.