[tahoe-lafs-trac-stream] [Tahoe-LAFS] #3412: Many tests are flaky

[Tahoe-LAFS]

#3412: Many tests are flaky
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     Reporter:  jaraco   |      Owner:  jaraco
         Type:  defect   |     Status:  assigned
     Priority:  normal   |  Milestone:  Support Python 3
    Component:  unknown  |    Version:  n/a
   Resolution:           |   Keywords:
Launchpad Bug:           |
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Comment (by jaraco):

 In the #twisted IRC channel, I got some advice from tos9, Glyph, and
 others regarding the fact that `trial` allows test methods to return a
 Deferred object, which may have one or more callbacks that will only be
 later executed, so wrapping those methods in `retry` will have little
 effect.

 I created [[https://github.com/jaraco/trial-retry|trial-retry]] to work
 out the kinks, and there I landed on a technique that seems to have the
 intended effect.

 Glyph had this to say about the approach:

 > Hopefully when we have some type-checking you'll get an error if you try
 to manipulate `.callbacks` like that
 > entirely "from the outside", i.e. if you have a Deferred which
 definitely isn't in the process of firing, you can probably get away with
 `.callbacks=something` but in the middle of execution this may have
 arbitrarily weird effects; running some callbacks twice, failing to run
 others

 It remains to be seen if the issue is merely theoretical or if such
 limitations might be triggered and in this codebase.

 Acknowledging this potential weakness of the approach, I plan to apply
 this technique to the work in progress and see if it improves the
 reliability of the test suite.

--
Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3412#comment:15>
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