unstable:Generator#next? returns false for empty generator
unstable:Generator#next? returns true for non-empty generator
unstable:Generator#next? returns true if the generator has not reached the end yet
unstable:Generator#next? returns false if the generator has reached the end
unstable:Generator#next? returns false if end? returns true
unstable:Generator#next raises an EOFError on empty generator
unstable:Generator#next raises an EOFError if no elements available
unstable:Generator#next raises an EOFError if end? returns true
unstable:Generator#next returns the element at the current position and moves forward
unstable:Generator#next subsequent calls should return all elements in proper order
