`ListCategory` sorts its completion by default, we are already building
the categories in the right order so don't need that.
The test tests the case of where you have 11 tabs and if the model was
sorted the tabs with index 10 and 11 would be sorted before the one with
index 2.
The `random.sample` bit for the tab url and title is to also make sure
the model isn't being sorted on those columns, whithout haveng to write
and all ten lines.
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