Tcp adaptor self test fails when all tests skipped

70: Test command: /usr/bin/python "/home/travis/build/apache/qpid-dispatch/build/tests/run.py" "-m" "unittest" "-v" "system_tests_tcp_adaptor"
70: Test timeout computed to be: 600
70: test_01_tcp_basic_connectivity (system_tests_tcp_adaptor.TcpAdaptor) ... skipped 'Python selectors module is not available on this platform.'
70: test_10_tcp_INTA_INTA_100 (system_tests_tcp_adaptor.TcpAdaptor) ... skipped 'Python selectors module is not available on this platform.'
70: test_11_tcp_INTA_INTA_1000 (system_tests_tcp_adaptor.TcpAdaptor) ... skipped 'Python selectors module is not available on this platform.'
70: test_12_tcp_INTA_INTA_500000 (system_tests_tcp_adaptor.TcpAdaptor) ... skipped 'Python selectors module is not available on this platform.'
70: test_13_tcp_EA1_EC2_500000 (system_tests_tcp_adaptor.TcpAdaptor) ... skipped 'Python selectors module is not available on this platform.'
70: test_20_tcp_connect_disconnect (system_tests_tcp_adaptor.TcpAdaptor) ... skipped 'Python selectors module is not available on this platform.'
70: test_50_concurrent (system_tests_tcp_adaptor.TcpAdaptor) ... skipped 'Python selectors module is not available on this platform.'
70: ERROR
70: 
70: ======================================================================
70: ERROR: tearDownClass (system_tests_tcp_adaptor.TcpAdaptor)
70: ----------------------------------------------------------------------
70: Traceback (most recent call last):
70:   File "/home/travis/build/apache/qpid-dispatch/tests/system_tests_tcp_adaptor.py", line 410, in tearDownClass
70:     server = cls.echo_servers[rtr]
70: AttributeError: type object 'TcpAdaptor' has no attribute 'echo_servers'
70: 
70: ----------------------------------------------------------------------
70: Ran 7 tests in 0.001s
70: 
70: FAILED (errors=1, skipped=7)
70/72 Test #70: system_tests_tcp_adaptor ..........................***Failed    0.07 sec