Disk drivers should be tested in both the raw and block device modes. For block device tests, create a new file system on the device. Then try to mount the new file system. Then try to perform multiple file operations.
The file system uses a page cache, so reading the same file over and over again does not really exercise the driver. The page cache can be forced to retrieve data from the device by memory-mapping the file with mmap(2). Then use msync(3C) to invalidate the in-memory copies.
Copy another (unmounted) partition of the same size to the raw device. Then use a command such as fsck(1M) to verify the correctness of the copy. The new partition can also be mounted and then later compared to the old partition on a file-by-file basis.