@@ -29,63 +29,62 @@
 if sys.platform == "win32":
     __all__.append("to_native_path_windows")
 
-from abc import abstractmethod
 import contextlib
-from functools import wraps
 import getpass
 import logging
 import ntpath
 import os
 import os.path as osp
-from pathlib import Path
 import platform
 import re
 import shutil
 import stat
 import subprocess
 import time
-from urllib.parse import urlsplit, urlunsplit
 import warnings
-
-# NOTE: Unused imports can be improved now that CI testing has fully resumed. Some of
-# these be used indirectly through other GitPython modules, which avoids having to write
-# gitdb all the time in their imports. They are not in __all__, at least currently,
-# because they could be removed or changed at any time, and so should not be considered
-# conceptually public to code outside GitPython. Linters of course do not like it.
-from gitdb.util import (
-    LazyMixin,  # noqa: F401
-    LockedFD,  # noqa: F401
-    bin_to_hex,  # noqa: F401
-    file_contents_ro,  # noqa: F401
-    file_contents_ro_filepath,  # noqa: F401
-    hex_to_bin,  # noqa: F401
-    make_sha,
-    to_bin_sha,  # noqa: F401
-    to_hex_sha,  # noqa: F401
-)
+from abc import abstractmethod
+from functools import wraps
+from pathlib import Path
 
 # typing ---------------------------------------------------------
-
 from typing import (
+    IO,
+    TYPE_CHECKING,
     Any,
     AnyStr,
     Callable,
     Dict,
     Generator,
-    IO,
     Iterator,
     List,
     Optional,
     Pattern,
     Sequence,
     Tuple,
-    TYPE_CHECKING,
     Type,
     TypeVar,
     Union,
     cast,
     overload,
 )
+from urllib.parse import urlsplit, urlunsplit
+
+# NOTE: Unused imports can be improved now that CI testing has fully resumed. Some of
+# these be used indirectly through other GitPython modules, which avoids having to write
+# gitdb all the time in their imports. They are not in __all__, at least currently,
+# because they could be removed or changed at any time, and so should not be considered
+# conceptually public to code outside GitPython. Linters of course do not like it.
+from gitdb.util import (
+    LazyMixin,  # noqa: F401
+    LockedFD,  # noqa: F401
+    bin_to_hex,  # noqa: F401
+    file_contents_ro,  # noqa: F401
+    file_contents_ro_filepath,  # noqa: F401
+    hex_to_bin,  # noqa: F401
+    make_sha,
+    to_bin_sha,  # noqa: F401
+    to_hex_sha,  # noqa: F401
+)
 
 if TYPE_CHECKING:
     from git.cmd import Git
@@ -94,9 +93,9 @@
     from git.repo.base import Repo
 
 from git.types import (
+    HSH_TD,
     Files_TD,
     Has_id_attribute,
-    HSH_TD,
     Literal,
     PathLike,
     Protocol,
@@ -419,11 +418,13 @@ def _validate_repo_path(path: PathLike, mode: Union[int, None] = None) -> None:
             hfs_name = part.translate(_HFS_IGNORABLES).lower()
             if ntfs_name in (".git", "git~1") or hfs_name == ".git":
                 raise ValueError("Repository path aliases Git metadata: %r" % name)
-            aliases_gitmodules = (
-                ntfs_name == ".gitmodules" or hfs_name == ".gitmodules" or ntfs_name in _NTFS_DOTGITMODULES_SHORT_NAMES
-            )
-            if aliases_gitmodules and mode is not None and stat.S_ISLNK(mode):
-                raise ValueError("Symbolic link aliases the submodule configuration: %r" % name)
+            if mode is not None and stat.S_ISLNK(mode):
+                if (
+                    ntfs_name == ".gitmodules"
+                    or hfs_name == ".gitmodules"
+                    or ntfs_name in _NTFS_DOTGITMODULES_SHORT_NAMES
+                ):
+                    raise ValueError("Symbolic link aliases the submodule configuration: %r" % name)
 
 
 def assure_directory_exists(path: PathLike, is_file: bool = False) -> bool:
 
@@ -408,20 +408,26 @@ def _cmp_tree_index(self, tree, index):
 
     @with_rw_repo("0.1.6")
     def test_index_lock_handling(self, rw_repo):
-        def add_bad_blob():
-            rw_repo.index.add([Blob(rw_repo, b"f" * 20, "bad-permissions", "foo")])
-
-        try:
-            ## First, fail on purpose adding into index.
-            add_bad_blob()
-        except Exception as ex:
-            assert "required argument is not an integer" in str(ex)
-
-        ## The second time should not fail due to stray lock file.
-        try:
-            add_bad_blob()
-        except Exception as ex:
-            assert "index.lock' could not be obtained" not in str(ex)
+        index = rw_repo.index
+        index_path = Path(index.path)
+        lock_path = Path(str(index_path) + ".lock")
+        before = index_path.read_bytes()
+
+        def fail_serialize(stream, ignore_extension_data):
+            assert lock_path.exists()
+            stream.write(b"partial index")
+            raise OSError("simulated index write failure")
+
+        with mock.patch.object(IndexFile, "_serialize", side_effect=fail_serialize):
+            for _ in range(2):
+                with pytest.raises(OSError, match="simulated index write failure"):
+                    index.write()
+                assert not lock_path.exists()
+                assert index_path.read_bytes() == before
+
+        index.add([Blob(rw_repo, b"f" * 20, 0o100644, "foo")])
+        assert not lock_path.exists()
+        assert rw_repo.index.entries[("foo", 0)].mode == 0o100644
 
     @with_rw_repo("0.1.6")
     def test_read_tree_methods_reject_index_output(self, rw_repo):