I'm experience sporadic failures in the pymongo test suite. About 1 in 10 times I run it I see a failure of some kind in test_collection. test_large_limit() fails occasionally because the collection that it uses, pymongo_test.test somehow still contains data left over from the test_invalid_key_names() test. Sometimes there are 3 of the documents left from that test, sometimes 4. So instead of having the expected 2000 elements in the collection at the end of test_large_limit, there are 2003 or 2004. Here's what shows up in the log file during one failure:

Mon Jun 4 11:19:45 [initandlisten] connection accepted from 127.0.0.1:34261 #73243
Mon Jun 4 11:19:45 [conn73237] end connection 127.0.0.1:34258
Mon Jun 4 11:19:45 [conn73240] CMD: drop pymongo_test.test
Mon Jun 4 11:19:45 [conn73240] build index pymongo_test.test

Mon Jun 4 11:19:45 [conn73240] build index done 0 records 0.001 secs
Mon Jun 4 11:19:45 [conn73240] info: creating collection pymongo_test.test on add index
Mon Jun 4 11:19:45 [conn73240] build index pymongo_test.test

Mon Jun 4 11:19:45 [conn73240] build index done 0 records 0.002 secs
Mon Jun 4 11:19:45 [conn73236] end connection 127.0.0.1:34257
Mon Jun 4 11:19:47 [conn6325] info DFM::findAll(): extent 0:af6000 was empty, skipping ahead. ns:stats.recent
Mon Jun 4 11:19:50 [FileAllocator] done allocating datafile /var/lib/mongod/pymongo_test.3, size: 512MB, took 4.861 secs
Mon Jun 4 11:20:37 [clientcursormon] mem (MB) res:1096 virt:10453 mapped:4959

I occasionally also see failures in test_distinct(), from what seems to be a related issue. The first insert in that test, test.save(

), seems to somehow happen before the drop_collection, so that when the collection is checked at the end of the test, that value is missing from the collection.

I've run the tests with --pdb-failures, and have checked db.error(), however there are none listed.