TestGraphStuff.testBasicSortTests is flaky

I tried again to run the above loop and this time I didn't get flakiness. Something across the stack might have changed in the meantime.

Oops, ignore the above comment, I was running the loop from within the branch containing the fix. The flakiness still occurs.

Same happens in the OpenBuildService. See the build results (which run the tests for python2 and python3) here: https://build.opensuse.org/package/show/devel:languages:python/python-testresources .
It fails with:

[ 45s] + PYTHONPATH=/home/abuild/rpmbuild/BUILDROOT/python-testresources-2.0.1-18.6.x86_64/usr/lib/python2.7/site-packages
[ 45s] + python2 -m testtools.run discover
[ 46s] Tests running...
[ 46s]
[ 46s] Ran 101 tests in 0.132s
[ 46s] OK
[ 46s] ++ '[' -f _current_flavor ']'
[ 46s] ++ cat _current_flavor
[ 46s] + python_flavor=python2
[ 46s] + '[' -z python2 ']'
[ 46s] + '[' python2 '!=' python3 ']'
[ 46s] + '[' -d build ']'
[ 46s] + mv build _build.python2
[ 46s] + '[' -d _build.python3 ']'
[ 46s] + mv _build.python3 build
[ 46s] + echo python3
[ 46s] + LANG=en_US.UTF-8
[ 46s] + PYTHONPATH=/home/abuild/rpmbuild/BUILDROOT/python-testresources-2.0.1-18.6.x86_64/usr/lib/python3.4/site-packages
[ 46s] + python3 -m testtools.run discover
[ 47s] Tests running...
[ 47s] ======================================================================
[ 47s] FAIL: testresources.tests.test_optimising_test_suite.TestGraphStuff.testBasicSortTests
[ 47s] ----------------------------------------------------------------------
[ 47s] Traceback (most recent call last):
[ 47s] File "/home/abuild/rpmbuild/BUILD/testresources-2.0.1/testresources/tests/test_optimising_test_suite.py", line 527, in testBasicSortTests
[ 47s] "failed with permutation %s" % (permutation,))
[ 47s] File "/usr/lib/python3.4/site-packages/testtools/testcase.py", line 417, in assertIn
[ 47s] self.assertThat(haystack, Contains(needle), message)
[ 47s] File "/usr/lib/python3.4/site-packages/testtools/testcase.py", line 498, in assertThat
[ 47s] raise mismatch_error
[ 47s] testtools.matchers._impl.MismatchError: [test_three, test_one, test_two, test_four] not in [[test_one, test_two, test_three, test_four], [test_three, test_two, test_one, test_four]]: failed with permutation [test_one, test_two, test_three, test_four]
[ 47s]
[ 47s] Ran 101 tests in 0.142s
[ 47s] FAILED (failures=1)
[ 47s] error: Bad exit status from /var/tmp/rpm-tmp.p4tsfj (%check)