NServiceBus: How to test a Bus.Defer()

does anybody know how to check (in a unit test) if a Bus.Defer has happened? It seems this it's not enough

Test.Saga(mySaga).ExpectSend < MessageThatIsDeferred >()

The result is:

ExpectedSendInvocation< MessageThatIsDeferred > not fulfilled Calls made: DeferMessageInvocation< MessageThatIsDeferred,System.DateTime >

Thanks, Miguel