Use Path() objects to store conftest files

Using Path().resolve() is better than py.path.realpath because
it resolves to the correct path/drive in case-insensitive file systems (pytest-dev#5792):

>>> from py.path import local
>>> from pathlib import Path
>>>
>>> local('d:\\projects').realpath()
local('d:\\projects')
>>> Path('d:\\projects').resolve()
WindowsPath('D:/projects')

Fix pytest-dev#5819

src/_pytest/config/__init__.py

@@ -414,10 +414,7 @@ def _getconftestmodules(self, path):
                 continue
             conftestpath = parent.join("conftest.py")
             if conftestpath.isfile():
-                # Use realpath to avoid loading the same conftest twice
-                # with build systems that create build directories containing
-                # symlinks to actual files.
-                mod = self._importconftest(conftestpath.realpath())
+                mod = self._importconftest(conftestpath)
                 clist.append(mod)
         self._dirpath2confmods[directory] = clist
         return clist
@@ -432,8 +429,14 @@ def _rget_with_confmod(self, name, path):
         raise KeyError(name)
 
     def _importconftest(self, conftestpath):
+        # Use a resolved Path object as key to avoid loading the same conftest twice
+        # with build systems that create build directories containing
+        # symlinks to actual files.
+        # Using Path().resolve() is better than py.path.realpath because
+        # it resolves to the correct path/drive in case-insensitive file systems (#5792)
+        key = Path(str(conftestpath)).resolve()
         try:
-            return self._conftestpath2mod[conftestpath]
+            return self._conftestpath2mod[key]
         except KeyError:
             pkgpath = conftestpath.pypkgpath()
             if pkgpath is None:
@@ -450,7 +453,7 @@ def _importconftest(self, conftestpath):
                 raise ConftestImportFailure(conftestpath, sys.exc_info())
 
             self._conftest_plugins.add(mod)
-            self._conftestpath2mod[conftestpath] = mod
+            self._conftestpath2mod[key] = mod
             dirpath = conftestpath.dirpath()
             if dirpath in self._dirpath2confmods:
                 for path, mods in self._dirpath2confmods.items():

testing/test_conftest.py

@@ -1,4 +1,6 @@
+import os
 import textwrap
+from pathlib import Path
 
 import py
 
@@ -163,11 +165,12 @@ def test_setinitial_conftest_subdirs(testdir, name):
     subconftest = sub.ensure("conftest.py")
     conftest = PytestPluginManager()
     conftest_setinitial(conftest, [sub.dirpath()], confcutdir=testdir.tmpdir)
+    key = Path(str(subconftest)).resolve()
     if name not in ("whatever", ".dotdir"):
-        assert subconftest in conftest._conftestpath2mod
+        assert key in conftest._conftestpath2mod
         assert len(conftest._conftestpath2mod) == 1
     else:
-        assert subconftest not in conftest._conftestpath2mod
+        assert key not in conftest._conftestpath2mod
         assert len(conftest._conftestpath2mod) == 0
 
 
@@ -275,6 +278,31 @@ def fixture():
     assert result.ret == ExitCode.OK
 
 
+@pytest.mark.skipif(
+    os.path.normcase("x") != os.path.normcase("X"),
+    reason="only relevant for case insensitive file systems",
+)
+def test_conftest_badcase(testdir):
+    """Check conftest.py loading when directory casing is wrong."""
+    testdir.tmpdir.mkdir("JenkinsRoot").mkdir("test")
+    source = {"setup.py": "", "test/__init__.py": "", "test/conftest.py": ""}
+    testdir.makepyfile(**{"JenkinsRoot/%s" % k: v for k, v in source.items()})
+
+    testdir.tmpdir.join("jenkinsroot/test").chdir()
+    result = testdir.runpytest()
+    assert result.ret == ExitCode.NO_TESTS_COLLECTED
+
+
+def test_conftest_uppercase(testdir):
+    """Check conftest.py loading when directory casing is wrong."""
+    source = {"__init__.py": "", "Foo/conftest.py": "", "Foo/__init__.py": ""}
+    testdir.makepyfile(**source)
+
+    testdir.tmpdir.chdir()
+    result = testdir.runpytest()
+    assert result.ret == ExitCode.NO_TESTS_COLLECTED
+
+
 def test_no_conftest(testdir):
     testdir.makeconftest("assert 0")
     result = testdir.runpytest("--noconftest")