Say out loud that these cells need a case sensitive filesystem

The Hub branch of check_model_quantization_status is only reachable when
os.path.exists(name) misses while check_local_model_exists(name) hits, and a case
difference is the only thing that produces that: case insensitive matching is the
entire purpose of that helper, so there is no filesystem independent way to write
the shape. `Outputs/MyModel` against an on-disk `outputs/mymodel` is it.

On macOS APFS and Windows NTFS os.path.exists answers True for `Outputs/MyModel`,
so the local branch is taken and the Hub round trip these five cells are named for
never happens. They would then pass while exercising nothing, which is the same
kind of quiet false confidence as a green check on tests CI never executed.

So probe the filesystem and skip with the reason, rather than leaving the
assumption implicit. On a case sensitive filesystem nothing changes: 28 passed,
no skips. Checked the guard both ways by substituting a case insensitive
os.path.exists, so it is not decorative.

Found by running the branch on macos-14 and windows-latest, which nothing in CI
does today.

Author: danielhanchen

tests/test_quant_status_transport_errors.py

@@ -41,6 +41,8 @@
 the two Hub entry points, so nothing touches the network.
 """
 
+import os
+
 import huggingface_hub
 import pytest
 import requests
@@ -328,6 +330,29 @@ def test_an_absent_local_config_still_reports_unquantized(tmp_path):
 _ON_DISK = ("outputs", "mymodel")
 
 
+def _require_a_case_sensitive_filesystem(tmp_path):
+    """State the precondition the shape above depends on, rather than assume it.
+
+    A case difference is the only thing that makes `os.path.exists(name)` miss
+    while `check_local_model_exists(name)` hits, because case insensitive matching
+    is the whole purpose of that helper. So there is no filesystem independent way
+    to write this shape, and on a case insensitive filesystem (macOS APFS, Windows
+    NTFS) `os.path.exists("Outputs/MyModel")` answers True, the local branch is
+    taken, and the Hub round trip these tests are named for never happens.
+
+    Left implicit, that turns them into tests that pass while exercising nothing.
+    Skipping says so out loud instead.
+    """
+    probe = tmp_path / "case_probe"
+    probe.mkdir(exist_ok = True)
+    if os.path.exists(str(tmp_path / "CASE_PROBE")):
+        pytest.skip(
+            "case insensitive filesystem: os.path.exists would resolve "
+            f"{_REQUESTED!r} locally and skip the Hub branch under test"
+        )
+    pass
+
+
 @pytest.mark.parametrize("save_method", ["merged_4bit", "forced_merged_4bit"])
 def test_local_4bit_still_resolves_when_only_the_config_fetch_fails(
     monkeypatch, tmp_path, save_method,
@@ -339,6 +364,7 @@ def test_local_4bit_still_resolves_when_only_the_config_fetch_fails(
         tmp_path.joinpath(*_ON_DISK),
         quant_config = {"load_in_4bit": True, "bnb_4bit_quant_type": "nf4"},
     )
+    _require_a_case_sensitive_filesystem(tmp_path)
     monkeypatch.chdir(tmp_path)
     _patch_ls_present(monkeypatch)
     _patch_config_fetch(monkeypatch, _RateLimited())
@@ -357,6 +383,7 @@ def test_local_4bit_plus_16bit_merge_still_raises(monkeypatch, tmp_path):
         tmp_path.joinpath(*_ON_DISK),
         quant_config = {"load_in_4bit": True, "bnb_4bit_quant_type": "nf4"},
     )
+    _require_a_case_sensitive_filesystem(tmp_path)
     monkeypatch.chdir(tmp_path)
     _patch_ls_present(monkeypatch)
     _patch_config_fetch(monkeypatch, _RateLimited())
@@ -372,6 +399,7 @@ def test_local_fp8_resolves_for_a_16bit_merge(monkeypatch, tmp_path):
         tmp_path.joinpath(*_ON_DISK),
         quant_config = {"quant_method": "fp8"},
     )
+    _require_a_case_sensitive_filesystem(tmp_path)
     monkeypatch.chdir(tmp_path)
     _patch_ls_present(monkeypatch)
     _patch_config_fetch(monkeypatch, _RateLimited())
@@ -385,6 +413,7 @@ def test_local_fp8_resolves_for_a_16bit_merge(monkeypatch, tmp_path):
 def test_no_local_copy_propagates(monkeypatch, tmp_path):
     """Nothing local can answer, so the outage is the whole story and must be
     what the caller sees, rather than a `(None, ...)` that writes no files."""
+    _require_a_case_sensitive_filesystem(tmp_path)
     monkeypatch.chdir(tmp_path)
     _patch_ls_present(monkeypatch)
     _patch_config_fetch(monkeypatch, _RateLimited())
@@ -403,6 +432,7 @@ def test_an_exactly_named_local_directory_never_reaches_the_config_fetch(
         tmp_path.joinpath(*_ON_DISK),
         quant_config = {"load_in_4bit": True, "bnb_4bit_quant_type": "nf4"},
     )
+    _require_a_case_sensitive_filesystem(tmp_path)
     monkeypatch.chdir(tmp_path)
     _patch_ls_present(monkeypatch)