Disable Twisted debugging in some tests

[jml]

Some of our tests assume that debugging is not enabled in Twisted. This makes that assumption explicit by disabling debugging for the duration of the test.

It does this by:

• changing the spinner to use a custom MonkeyPatch fixture, rather than testtools monkey patch
• making the fixture explicitly set debugging bools to a value (rather than hardcoding true or false)
• using a fixture always, but only the identity fixture (Fixture) when debugging is not set
• updating the relevant tests to use DebugTwisted(False)

Testing strategy has been to run tests with trial --debug-stacktraces. I don't think we need explicit tests for the debugging behavior. There are other issues preventing trial from running in full (due to Trial's weird reporter API), but that's a separate PR for another time.

Will conflict with #171, which also adds fixtures as a dependency, and (in spirit) with #202, which moves all Twisted code to its own package.

[rbtcollins]

If this can be landed now, lets do that and avoid juggling conflicts

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Review status: 0 of 6 files reviewed at latest revision, 4 unresolved discussions.

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_testtools/_deferreddebug.py, line 7 [r1] (raw file):_ No all ?

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_testtools/_deferreddebug.py, line 11 [r1] (raw file):_ PEP 297 (I think?) Specifically shows """ Foo bar baz""" for one liners. I value vertical space a lot - I realise its not a functional thing, but I'd like to keep this consistent, and I'm pretty sure we've done genuine one liners for everything in the code base...

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_testtools/_deferreddebug.py, line 17 [r1] (raw file):_ Since this is using _setUp, the dependency on fixtures should be versioned with minimum appropiate to the introduction of that API.

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_testtools/_deferreddebug.py, line 23 [r1] (raw file):_ I think this is fine as-is. It occurred to me reading it that you could instead say

def __init__(....)
    super
    self._deferred_debug = MoneyPatch('twisted.internet.defer.Deferred.debug', debug)
    self._delayedcall_debug = MonkeyPatch('twisted.internet.base.DelayedCall.debug', debug)

def _setUp(self):
    self.useFixture(self._deferred_debug)
    self.useFixture(self._delayedcall_debug)

Which seems a little clearer to me, but YMMW

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Comments from the review on Reviewable.io

[jml]

Thanks for the review. I've updated the docstring, and will merge.

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Review status: 0 of 6 files reviewed at latest revision, 4 unresolved discussions.

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_testtools/_deferreddebug.py, line 7 [r1] (raw file):_ No. I don't think it's quite so important for internal code. Can add one later if you feel strongly about it, or we have a coherent standard written somewhere.

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_testtools/_deferreddebug.py, line 11 [r1] (raw file):_ Yeah, we are. flocker follows this (Twisted-style) approach to docstrings and it creeped over.

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_testtools/_deferreddebug.py, line 17 [r1] (raw file):_ Done.

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Comments from the review on Reviewable.io

[jml]

Review status: 0 of 6 files reviewed at latest revision, 4 unresolved discussions, some commit checks failed.

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_testtools/_deferreddebug.py, line 23 [r1] (raw file):_ The way I wanted to write it was:

def debug_twisted(debug):
    return CompoundFixture([
        MonkeyPatch('twisted....', debug),
        MonkeyPatch('twisted....', debug),
    ])

It was this second use-case which provoked me to testing-cabal/fixtures#22

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Comments from the review on Reviewable.io

[jml]

Merged at 91c195c