Option added in conftest.py not available - leads to KeyError #416

.
│
└───foo
    │   conftest.py
    │
    └───unit
            test_stuff.py

============================= test session starts =============================
platform win32 -- Python 3.4.0 -- pytest-2.5.1
collected 1 items

foo/unit/test_stuff.py E

=================================== ERRORS ====================================
_________________________ ERROR at setup of test_slow _________________________

item = <Function 'test_slow'>

    def pytest_runtest_setup(item):
>       if 'slow' in item.keywords and not item.config.getvalue("runslow"):

foo\conftest.py:8:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <_pytest.config.Config object at 0x0000000002FAFB00>, name = 'runslow'
path = None

    def getvalue(self, name, path=None):
        """ return command line option value.

            :arg name: name of the command line option

            (deprecated) if we can't find the option also lookup
            the name in a matching conftest file.
            """
        try:
            return getattr(self.option, name)
        except AttributeError:
>           return self._getconftest(name, path, check=False)

c:\python\lib\site-packages\pytest-2.5.1-py3.4.egg\_pytest\config.py:807:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <_pytest.config.Config object at 0x0000000002FAFB00>, name = 'runslow'
path = None, check = False

    def _getconftest(self, name, path=None, check=False):
        if check:
            self._checkconftest(name)
>       return self._conftest.rget(name, path)

c:\python\lib\site-packages\pytest-2.5.1-py3.4.egg\_pytest\config.py:782:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <_pytest.config.Conftest object at 0x00000000035DD2B0>, name = 'runslow'
path = None

    def rget(self, name, path=None):
>       mod, value = self.rget_with_confmod(name, path)

c:\python\lib\site-packages\pytest-2.5.1-py3.4.egg\_pytest\config.py:516:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <_pytest.config.Conftest object at 0x00000000035DD2B0>, name = 'runslow'
path = None

    def rget_with_confmod(self, name, path=None):
        modules = self.getconftestmodules(path)
        modules.reverse()
        for mod in modules:
            try:
                return mod, getattr(mod, name)
            except AttributeError:
                continue
>       raise KeyError(name)
E       KeyError: 'runslow'

c:\python\lib\site-packages\pytest-2.5.1-py3.4.egg\_pytest\config.py:527: KeyError
=========================== 1 error in 0.08 seconds ===========================