[tahoe-lafs-trac-stream] [Tahoe-LAFS] #3918: Refactor MutableChecker tests

[Tahoe-LAFS]

#3918: Refactor MutableChecker tests
---------------------+---------------------------
 Reporter:  fenn-cs  |          Owner:
     Type:  defect   |         Status:  new
 Priority:  normal   |      Milestone:  undecided
Component:  unknown  |        Version:  n/a
 Keywords:           |  Launchpad Bug:
---------------------+---------------------------
 Update `MutableChecker` tests in src/allmydata/test/test_storage.py to
 either use `SyncTestCase` or `AsyncTestCas`e base test case and not
 unittest.TestCase

 This refactor would also involve using new and better assertion methods.

 Just like in [3917](https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3917)

--
Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3918>
Tahoe-LAFS <https://Tahoe-LAFS.org>
secure decentralized storage