Really, they do. They're sooooo important. But they're always the stuff people leave out.
One of the key things with a Database Testplan (for the AQA Applied A Level course btw) is that the plan needs to relate clearly to the evaluation criteria. This is totally like crucial dude - check out the markscheme AO4 Line 3.
So, you can have all of your generic testing stuff like field sizes, queries and whathaveyou, but if you don't have specific testing points related to your evaluation critieria you're not getting very far down the mark line.
Here are a couple of someone's evaluation criteria. We'll call him "Alex" (it's OK, he's not a duck...):
Test Number 11
Test: User can edit data (eval crit 2)
How tested: I will try to edit data in tables
Expected Outcome: Able to edit data
Test Number 12
Test: The database prints weekly and daily reports related to that week/day (eval crit 3)
How tested: I will try and print reports which automatically print the records for today or this week
Expected Outcome: The right data will be printed without anything which is not needed
Ideally you want to refer all of your evaluation criteria to points in your test plan. I'll say it again: this is in addition to the generic testing points that you might have. That's really important. Like, really.
Or the ducks will know.