[R]: fix bugs in unit test on FlashR core.
[R]: fix bugs in unit test on FlashR core.

flashxio/FlashX,icoming/FlashX,icoming/FlashX,flashxio/FlashX,flashxio/FlashX,icoming/FlashX,flashxio/FlashX,icoming/FlashX,flashxio/FlashX,flashxio/FlashX,icoming/FlashX