abstract fun cast(): IAssertionPlant<TSub>
Performs the down-cast if possible; reports a failure otherwise.
AssertionError - Might throw an AssertionError in case the down-cast cannot be performed
or an additionally specified assertion (using withLazyAssertions) does not hold.
IllegalStateException - In case reporting a failure does not throw itself.
Return
The newly created IAssertionPlant for the down-casted IAssertionPlant.subject.