Warn when writing or closing a cache file fails

AUTHORS

@@ -396,6 +396,7 @@ Pierre Sassoulas
 Pieter Mulder
 Piotr Banaszkiewicz
 Piotr Helm
+Poorva Barve
 Poulami Sau
 Prakhar Gurunani
 Praneeth Kodumagulla

changelog/15043.bugfix.rst

@@ -0,0 +1 @@
+Cache writes now emit :class:`pytest.PytestCacheWarning` when writing or closing the cache file fails, consistent with errors opening the file.

src/_pytest/cacheprovider.py

@@ -240,15 +240,13 @@ def set(self, key: str, value: object) -> None:
             return
         data = json.dumps(value, ensure_ascii=False, indent=2)
         try:
-            f = path.open("w", encoding="UTF-8")
+            with path.open("w", encoding="UTF-8") as f:
+                f.write(data)
         except OSError as exc:
             self.warn(
                 f"cache could not write path {path}: {exc}",
                 _ispytest=True,
             )
-        else:
-            with f:
-                f.write(data)
 
     def _ensure_cache_dir_and_supporting_files(self) -> None:
         """Create the cache dir and its supporting files."""

testing/test_cacheprovider.py

@@ -4,10 +4,12 @@
 from collections.abc import Sequence
 from enum import auto
 from enum import Enum
+import errno
 import os
 from pathlib import Path
 import shutil
 from typing import Any
+from unittest.mock import mock_open
 
 from _pytest.compat import assert_never
 from _pytest.config import ExitCode
@@ -104,6 +106,30 @@ def test_cache_writefail_cachefile_silent(self, pytester: Pytester) -> None:
         assert cache is not None
         cache.set("test/broken", [])
 
+    @pytest.mark.parametrize("failure", ["open", "write", "close"])
+    def test_cache_writefail_warns(
+        self, pytester: Pytester, monkeypatch: MonkeyPatch, failure: str
+    ) -> None:
+        config = pytester.parseconfigure()
+        cache = config.cache
+        assert cache is not None
+        cache.set("test/broken", [])
+        mocked_open = mock_open()
+        failing_operation = {
+            "open": mocked_open,
+            "write": mocked_open.return_value.write,
+            "close": mocked_open.return_value.__exit__,
+        }[failure]
+        failing_operation.side_effect = OSError(errno.ENOSPC, "No space left on device")
+
+        with monkeypatch.context() as m:
+            m.setattr(Path, "open", mocked_open)
+            with pytest.warns(
+                pytest.PytestCacheWarning,
+                match="cache could not write path .*: .*No space left on device",
+            ):
+                cache.set("test/broken", [])
+
     @pytest.fixture
     def unwritable_cache_dir(self, pytester: Pytester) -> Generator[Path]:
         cache_dir = pytester.path.joinpath(".pytest_cache")