tests: use more complex file storage test...
tests: use more complex file storage test
The previous test was attempting to to test delta storage behavior.
It didn't do a very good job at it because there was a good chance
a delta wasn't being used in storage.
Let's switch the test to yield a delta in storage so an upcoming
change to delegate delta logic to storage has the desired effect.
Differential Revision:
https://phab.mercurial-scm.org/D4723