Some notes:

• Weird to test dnd from the main "shouldList" method rather than

from a dedicated method (but all these pagemodel tests do that...)

• Weird to be testing dropping to the same destination for both tests

(1 and 2 source items). But that's what the old test was doing.

• There are other methods to port away from mocks, both here

and in alltaskspagemodeltest which I used as inspiration

Unittest