Change handling of root dir under Windows

- as Windows has no root dir as such, we use the
  current drive as root dir to better emulate the fs
- as in the real fs, if a path starts with a path separator,
  it points to the current drive (e.g. the root of cwd)
- fixes pytest-dev#673

Author: mrbean-bremen

pyfakefs/fake_filesystem.py

@@ -641,7 +641,8 @@ def home(cls):
                 home = os.path.join('C:', 'Users', username)
             else:
                 home = os.path.join('home', username)
-            cls.filesystem.create_dir(home)
+            if not cls.filesystem.exists(home):
+                cls.filesystem.create_dir(home)
         return cls(home.replace(os.sep, cls.filesystem.path_separator))
 
     def samefile(self, other_path):

pyfakefs/fake_pathlib.py

@@ -733,9 +733,11 @@ class PathlibTest(TestCase):
     @patchfs
     def test_cwd(self, fs):
         """Make sure fake file system is used for os in pathlib"""
-        self.assertEqual(os.path.sep, str(pathlib.Path.cwd()))
+        is_windows = sys.platform.startswith('win')
+        root_dir = 'C:' + os.path.sep if is_windows else os.path.sep
+        self.assertEqual(root_dir, str(pathlib.Path.cwd()))
         dot_abs = pathlib.Path(".").absolute()
-        self.assertEqual(os.path.sep, str(dot_abs))
+        self.assertEqual(root_dir, str(dot_abs))
         self.assertTrue(dot_abs.exists())
 
 
@@ -796,13 +798,13 @@ def setUp(self):
     def test_real_file_with_home(self):
         """Regression test for #558"""
         self.fs.is_windows_fs = os.name != 'nt'
+        if self.fs.is_windows_fs:
+            self.fs.is_macos = False
+        self.fs.reset()
         self.fs.add_real_file(__file__)
         with open(__file__) as f:
             self.assertTrue(f.read())
         home = Path.home()
-        if sys.version_info < (3, 6):
-            # fspath support since Python 3.6
-            home = str(home)
         os.chdir(home)
         with open(__file__) as f:
             self.assertTrue(f.read())
@@ -869,5 +871,13 @@ def test_drivelike_path(self):
         self.assertTrue(os.path.exists(str(file_path.relative_to(folder))))
 
 
+@unittest.skipIf(sys.platform != 'win32', 'Windows-specific behavior')
+class TestAbsolutePathOnWindows(fake_filesystem_unittest.TestCase):
+    @patchfs
+    def test_is_absolute(self, fs):
+        # regression test for #673
+        self.assertTrue(pathlib.Path(".").absolute().is_absolute())
+
+
 if __name__ == "__main__":
     unittest.main()

pyfakefs/tests/fake_filesystem_test.py

@@ -43,7 +43,7 @@ def _get_errno(raised_error):
 
 class TestCase(unittest.TestCase):
     is_windows = sys.platform.startswith('win')
-    _FAKE_FS_BASE = sep('/fakefs')
+    _FAKE_FS_BASE = 'C:\\fakefs' if is_windows else '/fakefs'
 
 
 class FakeFilesystemVsRealTest(TestCase):

pyfakefs/tests/fake_filesystem_unittest_test.py

@@ -106,9 +106,9 @@ def test_get_cwd(self):
         self.skip_real_fs()
         dirname = self.make_path('foo', 'bar')
         self.create_dir(dirname)
-        self.assertEqual(self.os.getcwd(), self.os.path.sep)
+        self.assertEqual(self.filesystem.root_dir_name, self.os.getcwd())
         self.os.chdir(dirname)
-        self.assertEqual(self.os.getcwd(), dirname)
+        self.assertEqual(dirname, self.os.getcwd())
 
     def test_listdir(self):
         self.assert_raises_os_error(

pyfakefs/tests/fake_filesystem_vs_real_test.py

@@ -77,7 +77,7 @@ def test_mkstemp_dir(self):
         self.assertEqual(2, len(temporary))
         self.assertEqual(next_fd, temporary[0])
         self.assertTrue(temporary[1].startswith(
-            os.path.join(os.sep, 'dir', 'tmp')))
+            os.path.join(self.fs.root_dir_name, 'dir', 'tmp')))
         self.assertTrue(self.fs.exists(temporary[1]))
         mode = 0o666 if self.fs.is_windows_fs else 0o600
         self.assertEqual(self.fs.get_object(temporary[1]).st_mode,