➜  nova git:(master) tox -e  py37  nova.tests.functional.test_servers
py37 develop-inst-nodeps: /home/steveguan/code/Openstack/nova
py37 installed: alembic==1.3.1,amqp==2.5.2,appdirs==1.4.3,attrs==19.3.0,automaton==1.17.0,Babel==2.7.0,bandit==1.6.2,bcrypt==3.1.7,cachetools==3.1.1,castellan==1.4.0,certifi==2019.11.28,cffi==1.13.2,chardet==3.0.4,cliff==2.16.0,cmd2==0.8.9,colorama==0.4.1,coverage==4.5.4,cryptography==2.8,cursive==0.2.2,ddt==1.2.2,debtcollector==1.22.0,decorator==4.4.1,dnspython==1.15.0,dogpile.cache==0.9.0,eventlet==0.25.1,extras==1.0.0,fasteners==0.14.1,fixtures==3.0.0,flake8==2.6.2,future==0.18.2,futurist==1.10.0,gabbi==1.49.0,gitdb2==2.0.6,GitPython==3.0.5,greenlet==0.4.15,hacking==1.1.0,idna==2.8,importlib-metadata==1.1.0,iso8601==0.1.12,Jinja2==2.10.3,jmespath==0.9.4,jsonpatch==1.24,jsonpath-rw==1.4.0,jsonpath-rw-ext==1.2.2,jsonpointer==2.0,jsonschema==3.2.0,keystoneauth1==3.18.0,keystonemiddleware==7.0.1,kombu==4.6.6,linecache2==1.0.0,lxml==4.4.2,Mako==1.1.0,MarkupSafe==1.1.1,mccabe==0.5.3,microversion-parse==0.2.1,mock==3.0.5,monotonic==1.5,more-itertools==8.0.0,mox3==0.28.0,msgpack==0.6.2,munch==2.5.0,netaddr==0.7.19,netifaces==0.10.9,networkx==2.4,-e git+https://github.com/openstack/nova.git@2f31c8d1b97c2b64581d8f824b6547f93dfd94fb#egg=nova,numpy==1.17.4,openstacksdk==0.38.0,os-brick==2.10.0,os-client-config==1.33.0,os-resource-classes==0.5.0,os-service-types==1.7.0,os-traits==2.0.0,os-vif==1.17.0,os-win==4.3.2,os-xenapi==0.3.4,osc-lib==1.14.1,oslo.cache==1.38.0,oslo.concurrency==3.31.0,oslo.config==6.12.0,oslo.context==2.23.0,oslo.db==5.0.2,oslo.i18n==3.25.0,oslo.log==3.45.0,oslo.messaging==10.4.0,oslo.middleware==3.38.1,oslo.policy==2.4.0,oslo.privsep==1.33.3,oslo.reports==1.30.0,oslo.rootwrap==5.16.1,oslo.serialization==2.29.2,oslo.service==1.40.2,oslo.upgradecheck==0.3.2,oslo.utils==3.42.1,oslo.versionedobjects==1.36.1,oslo.vmware==2.34.1,oslotest==3.8.1,osprofiler==2.9.0,ovs==2.11.0,ovsdbapp==0.18.0,packaging==19.2,paramiko==2.6.0,Paste==3.2.3,PasteDeploy==2.0.1,pbr==5.4.4,pluggy==0.13.1,ply==3.11,prettytable==0.7.2,psutil==5.6.7,psycopg2==2.8.4,py==1.8.0,pyasn1==0.4.8,pyasn1-modules==0.2.7,pycadf==2.10.0,pycodestyle==2.5.0,pycparser==2.19,pydot==1.4.1,pyflakes==1.2.3,pyinotify==0.9.6,PyJWT==1.7.1,PyMySQL==0.9.3,PyNaCl==1.3.0,pyOpenSSL==19.1.0,pyparsing==2.4.5,pyperclip==1.7.0,pypowervm==1.1.24,pyroute2==0.5.7,pyrsistent==0.15.6,pytest==5.3.1,python-barbicanclient==4.9.0,python-cinderclient==5.0.0,python-dateutil==2.8.1,python-editor==1.0.4,python-glanceclient==2.17.0,python-ironicclient==3.1.0,python-keystoneclient==3.22.0,python-mimeparse==1.6.0,python-neutronclient==6.14.0,python-subunit==1.3.0,pytz==2019.3,PyYAML==5.2,repoze.lru==0.7,requests==2.22.0,requests-mock==1.6.0,requestsexceptions==1.4.0,retrying==1.3.3,rfc3986==1.3.2,Routes==2.4.1,simplejson==3.17.0,six==1.13.0,smmap2==2.0.5,sortedcontainers==2.1.0,SQLAlchemy==1.3.11,sqlalchemy-migrate==0.13.0,sqlparse==0.3.0,statsd==3.3.0,stestr==2.5.1,stevedore==1.31.0,suds-jurko==0.6,taskflow==3.8.0,Tempita==0.5.2,tenacity==6.0.0,testresources==2.0.1,testscenarios==0.5.0,testtools==2.3.0,tooz==1.67.0,traceback2==1.4.0,unittest2==1.1.0,urllib3==1.25.7,vine==1.3.0,voluptuous==0.11.7,warlock==1.3.3,wcwidth==0.1.7,WebOb==1.8.5,websockify==0.9.0,wrapt==1.11.2,wsgi-intercept==1.9.1,yappi==1.0,zipp==0.6.0,zVMCloudConnector==1.4.1
py37 run-test-pre: PYTHONHASHSEED='2433496554'
py37 run-test: commands[0] | stestr run nova.tests.functional.test_servers
Modules with known eventlet monkey patching issues were imported prior to eventlet monkey patching: urllib3, oslo_context.context. This warning can usually be ignored if the caller is only importing and not executing nova code.
Exception ignored in: <function _after_fork at 0x7fd191b42dd0>
Traceback (most recent call last):
  File "/usr/lib/python3.7/threading.py", line 1373, in _after_fork
    assert len(_active) == 1
AssertionError: 
The specified regex doesn't match with anythingERROR: InvocationError for command /home/steveguan/code/Openstack/nova/.tox/py37/bin/stestr run nova.tests.functional.test_servers (exited with code 1)

i've faced the same error whiling making a unit test