Sure, but in that case I wouldn't test that the list contains exactly the 10 customers I expect, since that's not what the code is supposed to do. That's a shortcut you introduced while testing. I usually approach things like this with two assertions - that the size of the list under test increased by X, and that the newly created record(s) exist in the list.

After all, the code doesn't show the 10 most recent customers that purchased an item, it shows ALL customers. You could hide a pagination bug where only the first page of results functions if you wipe the database first.