move conftest visibility tests and their setup into a class, accomodates @nicoddemus 's comment

--HG--
branch : issue616

testing/test_conftest.py

@@ -259,9 +259,8 @@ def test_conftest_found_with_double_dash(testdir):
     """)
 
 
-# conftest visibility, related to issue616
-
-def _setup_tree(testdir):
+class TestConftestVisibility:
+    def _setup_tree(self, testdir):  # for issue616
         # example mostly taken from:
         # https://mail.python.org/pipermail/pytest-dev/2014-September/002617.html
         runner = testdir.mkdir("empty")
@@ -310,9 +309,9 @@ def _setup_tree(testdir):
             "swc": swc,
             "snc": snc}
 
-# N.B.: "swc" stands for "subdir with conftest.py"
-#       "snc" stands for "subdir no [i.e. without] conftest.py"
-@pytest.mark.parametrize("chdir,testarg,expect_ntests_passed", [
+    # N.B.: "swc" stands for "subdir with conftest.py"
+    #       "snc" stands for "subdir no [i.e. without] conftest.py"
+    @pytest.mark.parametrize("chdir,testarg,expect_ntests_passed", [
         ("runner",  "..",               3),
         ("package", "..",               3),
         ("swc",     "../..",            3),
@@ -332,11 +331,11 @@ def _setup_tree(testdir):
         ("package", "./snc",            1),
         ("swc",     "../snc",           1),
         ("snc",     ".",                1),
-])
-@pytest.mark.issue616
-def test_parsefactories_relative_node_ids(
-        testdir, chdir,testarg, expect_ntests_passed):
-    dirs = _setup_tree(testdir)
+    ])
+    @pytest.mark.issue616
+    def test_parsefactories_relative_node_ids(
+            self, testdir, chdir,testarg, expect_ntests_passed):
+        dirs = self._setup_tree(testdir)
         print("pytest run in cwd: %s" %(
               dirs[chdir].relto(testdir.tmpdir)))
         print("pytestarg        : %s" %(testarg))