Problem/Motivation
That test uses its own mock date formatter (with wrong arguments), it could just as well use the actual date string that it expects.
Also strange that time doesn't seem to be defined at all, would make more sense to explicityl define that and also explicitly assert the received arguments in the mocked method.
Proposed resolution
Hardcode the expected result, pass ['time' => $timestamp] as second argument to render() so it more closely reflects a real call.