Kalpak Shah [off-list ref] writes:

regression tests. It does the following:
1) Create an test fs and format it with ext2/3/4 and random selection of
features.
2) Mount it and copy data into it.
3) Move around the blocks of the filesystem randomly causing corruption.
Also overwrite some random blocks with garbage from /dev/urandom. Create
a copy of this corrupted filesystem.

If you use a normal pseudo random number generator and print the seed
(e.g. create from the time) initially the image can be easily recreated 
later without shipping it around. /dev/urandom
is not really needed for this since you don't need cryptographic
strength randomness. Besides urandom data is precious and it's 
a pity to use it up needlessly.

bash has $RANDOM built in for this purpose.

-Andi