first run

vagrant@precise64:~/devstack$ cd /opt/stack/nova
vagrant@precise64:/opt/stack/nova$ tox
GLOB sdist-make: /opt/stack/nova/setup.py
py26 create: /opt/stack/nova/.tox/py26
ERROR: InterpreterNotFound: python2.6
py27 create: /opt/stack/nova/.tox/py27
py27 installdeps: -r/opt/stack/nova/tools/pip-requires, -r/opt/stack/nova/tools/test-requires
py27 inst: /opt/stack/nova/.tox/dist/nova-2013.2.a28.ga92b7c8.zip
py27 runtests: commands[0]
py27 runtests: commands[1]
running testr
running=OS_STDOUT_CAPTURE=1 OS_STDERR_CAPTURE=1 OS_TEST_TIMEOUT=60 ${PYTHON:-python} -m subunit.run discover -t ./ ./nova/tests --list
running=OS_STDOUT_CAPTURE=1 OS_STDERR_CAPTURE=1 OS_TEST_TIMEOUT=60 ${PYTHON:-python} -m subunit.run discover -t ./ ./nova/tests  --load-list /tmp/tmpS3OBYH
running=OS_STDOUT_CAPTURE=1 OS_STDERR_CAPTURE=1 OS_TEST_TIMEOUT=60 ${PYTHON:-python} -m subunit.run discover -t ./ ./nova/tests  --load-list /tmp/tmpZPpaEg
Unimplemented block at ../../relaxng.c:3824
Ran 5481 tests in 329.349s
PASSED (id=0, skips=13)
Slowest Tests
Test id                                                                                           Runtime (s)
------------------------------------------------------------------------------------------------  -----------
nova.tests.servicegroup.test_mc_servicegroup.MemcachedServiceGroupTestCase.test_memcached_driver  8.039
nova.tests.servicegroup.test_db_servicegroup.DBServiceGroupTestCase.test_DB_driver                8.031
nova.tests.test_migrations.TestNovaMigrations.test_walk_versions                                  4.888
nova.tests.api.ec2.test_cloud.CloudTestCase.test_instance_initiated_shutdown_behavior             3.619
nova.tests.integrated.test_servers.ServersTest.test_deferred_delete                               2.825
nova.tests.integrated.test_servers.ServersTest.test_create_multiple_servers                       2.674
nova.tests.integrated.test_api_samples.ServersActionsAllXmlTest.test_server_revert_resize         2.616
nova.tests.integrated.test_api_samples.ServersActionsAllJsonTest.test_server_revert_resize        2.573
nova.tests.integrated.test_api_samples.ServersActionsAllXmlTest.test_server_confirm_resize        2.434
nova.tests.integrated.test_api_samples.ServersActionsAllJsonTest.test_server_confirm_resize       2.411
pep8 create: /opt/stack/nova/.tox/pep8
pep8 installdeps: -r/opt/stack/nova/tools/pip-requires, -r/opt/stack/nova/tools/test-requires
pep8 inst: /opt/stack/nova/.tox/dist/nova-2013.2.a28.ga92b7c8.zip
pep8 runtests: commands[0]
WARNING:test command found but not installed in testenv
  cmd: /bin/bash
  env: /opt/stack/nova/.tox/pep8
Maybe forgot to specify a dependency?
199 passed and 0 failed.
Test passed.
3 imports missing in this test environment
9 imports missing in this test environment
_____________________________________________ summary ______________________________________________
ERROR:   py26: InterpreterNotFound: python2.6
  py27: commands succeeded
  pep8: commands succeeded

second run, nothing in between

vagrant@precise64:/opt/stack/nova$ tox
GLOB sdist-make: /opt/stack/nova/setup.py
py26 create: /opt/stack/nova/.tox/py26
ERROR: InterpreterNotFound: python2.6
py27 inst-nodeps: /opt/stack/nova/.tox/dist/nova-2013.2.a28.ga92b7c8.zip
py27 runtests: commands[0]
py27 runtests: commands[1]
running testr
running=OS_STDOUT_CAPTURE=1 OS_STDERR_CAPTURE=1 OS_TEST_TIMEOUT=60 ${PYTHON:-python} -m subunit.run discover -t ./ ./nova/tests --list
running=OS_STDOUT_CAPTURE=1 OS_STDERR_CAPTURE=1 OS_TEST_TIMEOUT=60 ${PYTHON:-python} -m subunit.run discover -t ./ ./nova/tests  --load-list /tmp/tmpZawSiq
running=OS_STDOUT_CAPTURE=1 OS_STDERR_CAPTURE=1 OS_TEST_TIMEOUT=60 ${PYTHON:-python} -m subunit.run discover -t ./ ./nova/tests  --load-list /tmp/tmpIbngjG
Unimplemented block at ../../relaxng.c:3824
Ran 5481 tests in 326.655s (-2.694s)
PASSED (id=1, skips=13)
Slowest Tests
Test id                                                                                           Runtime (s)
------------------------------------------------------------------------------------------------  -----------
nova.tests.servicegroup.test_mc_servicegroup.MemcachedServiceGroupTestCase.test_memcached_driver  8.042
nova.tests.servicegroup.test_db_servicegroup.DBServiceGroupTestCase.test_DB_driver                8.031
nova.tests.test_migrations.TestNovaMigrations.test_walk_versions                                  5.277
nova.tests.api.ec2.test_cloud.CloudTestCase.test_instance_initiated_shutdown_behavior             3.782
nova.tests.integrated.test_servers.ServersTest.test_create_multiple_servers                       2.961
nova.tests.integrated.test_api_samples.ServersActionsAllXmlTest.test_server_revert_resize         2.831
nova.tests.integrated.test_servers.ServersTest.test_deferred_delete                               2.829
nova.tests.integrated.test_api_samples.ServersActionsAllJsonTest.test_server_revert_resize        2.684
nova.tests.integrated.test_api_samples.ServersActionsAllXmlTest.test_server_confirm_resize        2.435
nova.tests.integrated.test_api_samples.ServersActionsAllJsonTest.test_server_confirm_resize       2.397
pep8 inst-nodeps: /opt/stack/nova/.tox/dist/nova-2013.2.a28.ga92b7c8.zip
pep8 runtests: commands[0]
WARNING:test command found but not installed in testenv
  cmd: /bin/bash
  env: /opt/stack/nova/.tox/pep8
Maybe forgot to specify a dependency?
199 passed and 0 failed.
Test passed.
3 imports missing in this test environment
9 imports missing in this test environment
________________________________________________________ summary _________________________________________________________
ERROR:   py26: InterpreterNotFound: python2.6
  py27: commands succeeded
  pep8: commands succeeded