Fix incorrect exception on opening non-existing directory

- fixes #986

Author: mrbean-bremen

pyfakefs/fake_os.py

@@ -254,7 +254,11 @@ def open(
         has_directory_flag = (
             hasattr(os, "O_DIRECTORY") and flags & os.O_DIRECTORY == os.O_DIRECTORY
         )
-        if has_directory_flag and not self.filesystem.isdir(path):
+        if (
+            has_directory_flag
+            and self.filesystem.exists(path)
+            and not self.filesystem.isdir(path)
+        ):
             raise OSError(errno.ENOTDIR, "path is not a directory", path)
 
         has_follow_flag = (

pyfakefs/tests/fake_os_test.py

@@ -605,8 +605,10 @@ def test_open_raises_with_trailing_separator_windows(self):
         self.check_open_raises_with_trailing_separator(errno.EINVAL)
 
     @unittest.skipIf(not hasattr(os, "O_DIRECTORY"), "opening directory not supported")
-    def test_open_raises_if_not_dir(self):
+    def test_open_with_o_directory(self):
         self.check_posix_only()
+        with self.assertRaises(FileNotFoundError):
+            self.os.open("bogus", os.O_RDONLY | os.O_DIRECTORY)
         file_path = self.make_path("file.txt")
         self.create_file(file_path, contents="foo")
         with self.assertRaises(NotADirectoryError):