testing - How do I force ext3 partition to the "error" state?

I have a script where fsck is called in case filesystem is in "error" state only.
I'd like to tests it.
Unfortunatelly I don't know how to force "error" state on ext3 partition.

The only one idea I have is run fsck on mounted partition first. AS soon as there is warning that filesystem can be damaged, I expect it can help. Need to try.

Meanwhile, may be anyone knows answer already?