stem unit tests fail on Tor 0.2.9, which is still supported until 1 January 2020
client.connection... failed (0.05s)
test_connection_time 25 ms [SUCCESS]
test_established [FAILURE]
test_invalid_arguments 1 ms [SUCCESS]
test_no_common_link_protocol 9 ms [SUCCESS]
test_not_orport 1 ms [SUCCESS]
======================================================================
FAIL: test_established
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/travis/build/teor2345/stem/test/integ/client/connection.py", line 66, in test_established
self.assertEqual(5, int(conn.link_protocol))
AssertionError: 5 != 4
----------------------------------------------------------------------
Ran 5 tests in 0.042s
FAILED (failures=1)
https://travis-ci.org/teor2345/stem/jobs/536613171#L1865
Link protocol 4 is supported by 0.2.9, and 5 is supported by 0.3.1.1-alpha and later: https://gitweb.torproject.org/torspec.git/tree/tor-spec.txt#n1984