<commit_before>A session-fixture which can look at all collected tests
----------------------------------------------------------------

A session-scoped fixture effectively has access to all 
collected test items.  Here is an example of a fixture
function which walks all collected tests and looks
if their test class defines a ``callme`` method and
calls it::

    # content of conftest.py

    import pytest

    @pytest.fixture(scope="session", autouse=True)
    def callattr_ahead_of_alltests(request):
        print "callattr_ahead_of_alltests called"
        seen = set([None])
        session = request.node
        for item in session.items:
            cls = item.getparent(pytest.Class)
            if cls not in seen:
                if hasattr(cls.obj, "callme"):
                   cls.obj.callme()
                seen.add(cls)

test classes may now define a ``callme`` method which
will be called ahead of running any tests::

    # content of test_module.py

    class TestHello:
        @classmethod
        def callme(cls):
            print "callme called!"

        def test_method1(self):
            print "test_method1 called"
        
        def test_method2(self):
            print "test_method1 called"

    class TestOther:
        @classmethod
        def callme(cls):
            print "callme other called"
        def test_other(self):
            print "test other"

    # works with unittest as well ...
    import unittest
    
    class SomeTest(unittest.TestCase):
        @classmethod
        def callme(self):
            print "SomeTest callme called"

        def test_unit1(self):
            print "test_unit1 method called"

If you run this without output capturing::

    $ py.test -q -s test_module.py 
    Traceback (most recent call last):
      File "/home/hpk/p/pytest/.tox/regen/lib/python3.4/site-packages/_pytest/config.py", line 513, in getconftestmodules
        return self._path2confmods[path]
    KeyError: local('/tmp/doc-exec-88/test_module.py')
    
    During handling of the above exception, another exception occurred:
    Traceback (most recent call last):
      File "/home/hpk/p/pytest/.tox/regen/lib/python3.4/site-packages/_pytest/config.py", line 537, in importconftest
        return self._conftestpath2mod[conftestpath]
    KeyError: local('/tmp/doc-exec-88/conftest.py')
    
    During handling of the above exception, another exception occurred:
    Traceback (most recent call last):
      File "/home/hpk/p/pytest/.tox/regen/lib/python3.4/site-packages/_pytest/config.py", line 543, in importconftest
        mod = conftestpath.pyimport()
      File "/home/hpk/p/pytest/.tox/regen/lib/python3.4/site-packages/py/_path/local.py", line 640, in pyimport
        __import__(modname)
      File "/tmp/doc-exec-88/conftest.py", line 6
        print "callattr_ahead_of_alltests called"
                                                ^
    SyntaxError: invalid syntax
    ERROR: could not load /tmp/doc-exec-88/conftest.py
    <commit_msg>fix issue584: fix py3 syntax errors for example/special.txt. Thanks <NAME>.<commit_after>A session-fixture which can look at all collected tests
----------------------------------------------------------------

A session-scoped fixture effectively has access to all
collected test items.  Here is an example of a fixture
function which walks all collected tests and looks
if their test class defines a ``callme`` method and
calls it::

    # content of conftest.py

    import pytest

    @pytest.fixture(scope="session", autouse=True)
    def callattr_ahead_of_alltests(request):
        print ("callattr_ahead_of_alltests called")
        seen = set([None])
        session = request.node
        for item in session.items:
            cls = item.getparent(pytest.Class)
            if cls not in seen:
                if hasattr(cls.obj, "callme"):
                   cls.obj.callme()
                seen.add(cls)

test classes may now define a ``callme`` method which
will be called ahead of running any tests::

    # content of test_module.py

    class TestHello:
        @classmethod
        def callme(cls):
            print ("callme called!")

        def test_method1(self):
            print ("test_method1 called")

        def test_method2(self):
            print ("test_method1 called")

    class TestOther:
        @classmethod
        def callme(cls):
            print ("callme other called")
        def test_other(self):
            print ("test other")

    # works with unittest as well ...
    import unittest

    class SomeTest(unittest.TestCase):
        @classmethod
        def callme(self):
            print ("SomeTest callme called")

        def test_unit1(self):
            print ("test_unit1 method called")

If you run this without output capturing::

    $ py.test -q -s test_module.py
    callattr_ahead_of_alltests called
    callme called!
    callme other called
    SomeTest callme called
    test_method1 called
    .test_method1 called
    .test other
    .test_unit1 method called
    .
    4 passed in 0.05 seconds
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