[tahoe-lafs-trac-stream] [Tahoe-LAFS] #2290: allmydata.test.test_util.FileUtil.test_disk_stats sometimes fails on Travis

[Tahoe-LAFS]

#2290: allmydata.test.test_util.FileUtil.test_disk_stats sometimes fails on Travis
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     Reporter:  daira   |      Owner:
         Type:  defect  |     Status:  new
     Priority:  normal  |  Milestone:  undecided
    Component:  code    |    Version:  1.10.0
   Resolution:          |   Keywords:  tests travis
Launchpad Bug:          |
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Comment (by warner):

 #2298 was a dup.

 After some more investigation, it appears that Travis-CI workers sometimes
 report fake-looking `os.statvfs()` values. I've filed an issue to
 investigate:

   https://github.com/travis-ci/travis-ci/issues/2788

 On the job that failed, every single `os.statvfs()` call for the whole
 20-minute test suite claimed that the 20 GiB disk was empty (`f_bfree ==
 f_blocks`). On passing jobs, f_blocks reported a 120 GiB disk (or larger)
 and the number of free blocks rose and fell over the course of the test
 run.

 My hunch is that some of the travis workers are using a virtual disk that
 happens to return bogus or simulated data to `os.statvfs()`. Daira and I
 decided that it'd be ok to relax this test (to accept `disk["used"] >=
 0`). If the Travis folks find an easy solution, we can tighten the test
 back up again.

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2290#comment:2>
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