pytest 3.6: ValueError: fixture is being applied more than once to the same function

[hroncok]

$ tox -r -e py36
GLOB sdist-make: .../pytest-httpbin/setup.py
py36 recreate: .../pytest-httpbin/.tox/py36
py36 installdeps: pytest, requests
py36 inst: .../pytest-httpbin/.tox/dist/pytest-httpbin-0.3.0.zip
py36 installed: atomicwrites==1.1.5,attrs==18.1.0,blinker==1.4,brotlipy==0.7.0,certifi==2018.4.16,cffi==1.11.5,chardet==3.0.4,click==6.7,decorator==4.3.0,Flask==1.0.2,httpbin==0.7.0,idna==2.7,itsdangerous==0.24,Jinja2==2.10,MarkupSafe==1.0,more-itertools==4.2.0,pluggy==0.6.0,py==1.5.3,pycparser==2.18,pytest==3.6.1,pytest-httpbin==0.3.0,raven==6.9.0,requests==2.19.1,six==1.11.0,urllib3==1.23,Werkzeug==0.14.1
py36 runtests: PYTHONHASHSEED='1646700043'
py36 runtests: commands[0] | ./runtests.sh tests/
Traceback (most recent call last):
  File ".../pytest-httpbin/.tox/py36/lib/python3.6/site-packages/_pytest/config.py", line 355, in _getconftestmodules
    return self._path2confmods[path]
KeyError: local('.../pytest-httpbin/tests')

During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File ".../pytest-httpbin/.tox/py36/lib/python3.6/site-packages/_pytest/config.py", line 386, in _importconftest
    return self._conftestpath2mod[conftestpath]
KeyError: local('.../pytest-httpbin/tests/conftest.py')

During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File ".../pytest-httpbin/.tox/py36/lib/python3.6/site-packages/_pytest/config.py", line 392, in _importconftest
    mod = conftestpath.pyimport()
  File ".../pytest-httpbin/.tox/py36/lib/python3.6/site-packages/py/_path/local.py", line 668, in pyimport
    __import__(modname)
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 656, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 626, in _load_backward_compatible
  File ".../pytest-httpbin/.tox/py36/lib/python3.6/site-packages/_pytest/assertion/rewrite.py", line 216, in load_module
    py.builtin.exec_(co, mod.__dict__)
  File ".../pytest-httpbin/tests/conftest.py", line 6, in <module>
    pytest.fixture(autouse=True)(httpbin_ca_bundle)
  File ".../pytest-httpbin/.tox/py36/lib/python3.6/site-packages/_pytest/fixtures.py", line 900, in __call__
    "fixture is being applied more than once to the same function"
ValueError: fixture is being applied more than once to the same function
ERROR: could not load .../pytest-httpbin/tests/conftest.py

ERROR: InvocationError: '.../pytest-httpbin/runtests.sh tests/'
___________________________________ summary ____________________________________
ERROR:   py36: commands failed

See also pytest-dev/pytest#3518