ChannelHandler creates an EventHandler that adds the event to the provided channel.
Expect polls the channel for the next event and returns it. Fails the test if no event found.
ExpectNone polls the channel and fails the test if any events are available.
ExpectOne polls the channel and ensures that only a single event is available. Fails the test if the number of events != 1.
Poll polls the channel to see if there is an event waiting. Returns either the next event or nil.