try fixing config test

dvc/config.py

@@ -1,6 +1,8 @@
 """DVC config objects."""
 
+import ntpath
 import os
+import posixpath
 import re
 from contextlib import contextmanager
 from functools import partial
@@ -268,12 +270,17 @@ def _resolve(conf_dir, path):
         if re.match(r"\w+://", path):
             return path
 
+        if os.name == "nt" and posixpath.isabs(path) and ntpath.sep not in path:
+            return path
+
         if os.path.isabs(path):
             return path
 
         # on windows convert slashes to backslashes
         # to have path compatible with abs_conf_dir
         if os.path.sep == "\\" and "/" in path:
+            if path.startswith("/"):
+                path = path.replace("/", "\\\\", 1)
             path = path.replace("/", "\\")
 
         expanded = os.path.expanduser(path)
@@ -305,6 +312,9 @@ def _to_relpath(conf_dir, path):
         if os.path.expanduser(path) != path:
             return localfs.as_posix(path)
 
+        if os.name == "nt" and posixpath.isabs(path) and ntpath.sep not in path:
+            return path
+
         if isinstance(path, RelPath) or not os.path.isabs(path):
             path = relpath(path, conf_dir)
             return localfs.as_posix(path)

dvc/fs/dvc.py

@@ -732,9 +732,10 @@ def repo_url(self) -> str:
         return self.fs.repo_url
 
     def from_os_path(self, path: str) -> str:
-        if os.path.isabs(path):
+        if os.path.isabs(path) or (
+            os.name == "nt" and posixpath.isabs(path) and ntpath.sep not in path
+        ):
             path = os.path.relpath(path, self.repo.root_dir)
-
         return as_posix(path)
 
     def close(self):

tests/unit/test_ignore.py

@@ -168,7 +168,7 @@ def test_match_ignore_from_file(
 ):
     from dvc.fs import localfs
 
-    root = os.path.sep * (2 if os.name == "nt" else 1)
+    root = r"\\" if os.name == "nt" else "/"
     dvcignore_path = os.path.join(
         root, "full", "path", "to", "ignore", "file", ".dvcignore"
     )