try to override unittest methods

src/pymatgen/util/testing/__init__.py

@@ -10,16 +10,15 @@
 import json
 import pickle  # use pickle, not cPickle so that we get the traceback in case of errors
 import string
-import warnings
 from pathlib import Path
 from typing import TYPE_CHECKING
-from unittest import TestCase
 
 import pytest
 from monty.json import MontyDecoder, MontyEncoder, MSONable
 from monty.serialization import loadfn
 
 from pymatgen.core import ROOT, SETTINGS, Structure
+from pymatgen.util.testing._temp_testcase import _TempTestCase4Migrate
 
 if TYPE_CHECKING:
     from collections.abc import Sequence
@@ -36,23 +35,12 @@
 FAKE_POTCAR_DIR = f"{VASP_IN_DIR}/fake_potcars"
 
 
-class PymatgenTest(TestCase):
+class PymatgenTest(_TempTestCase4Migrate):
     """Extends unittest.TestCase with several assert methods for array and str comparison."""
 
     # dict of lazily-loaded test structures (initialized to None)
     TEST_STRUCTURES: ClassVar[dict[str | Path, Structure | None]] = dict.fromkeys(STRUCTURES_DIR.glob("*"))
 
-    @classmethod
-    def setUpClass(cls):
-        """Issue a FutureWarning, see PR 4209."""
-        warnings.warn(
-            "PymatgenTest is scheduled for migration to pytest after 2026-01-01. "
-            "Please adapt your tests accordingly.",
-            FutureWarning,
-            stacklevel=2,
-        )
-        super().setUpClass()
-
     @pytest.fixture(autouse=True)  # make all tests run a in a temporary directory accessible via self.tmp_path
     def _tmp_dir(self, tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> None:
         # https://pytest.org/en/latest/how-to/unittest.html#using-autouse-fixtures-and-accessing-other-fixtures

src/pymatgen/util/testing/_temp_testcase.py

@@ -0,0 +1,82 @@
+# ruff: noqa: PT009, PT027
+
+
+from __future__ import annotations
+
+import warnings
+from unittest import TestCase
+
+
+class _TempTestCase4Migrate(TestCase):
+    """Temporary TestCase for migration to `pytest` framework,
+    inserted FutureWarning for unittest.TestCase-specific methods.
+    """
+
+    def _issue_warning(self, method_name):
+        warnings.warn(
+            f"unittest {method_name=} will not be supported by pytest after migration by 2026-01-01, see PR4209.",
+            FutureWarning,
+            stacklevel=2,
+        )
+
+    def setUp(self, *args, **kwargs):
+        self._issue_warning("setUp")
+        super().setUp(*args, **kwargs)
+
+    def tearDown(self, *args, **kwargs):
+        self._issue_warning("tearDown")
+        super().tearDown(*args, **kwargs)
+
+    @classmethod
+    def setUpClass(cls, *args, **kwargs):
+        cls._issue_warning("setUpClass")
+        super().setUpClass(*args, **kwargs)
+
+    @classmethod
+    def tearDownClass(cls, *args, **kwargs):
+        cls._issue_warning("tearDownClass")
+        super().tearDownClass(*args, **kwargs)
+
+    def assertEqual(self, *args, **kwargs):
+        self._issue_warning("assertEqual")
+        return super().assertEqual(*args, **kwargs)
+
+    def assertNotEqual(self, *args, **kwargs):
+        self._issue_warning("assertNotEqual")
+        return super().assertNotEqual(*args, **kwargs)
+
+    def assertTrue(self, *args, **kwargs):
+        self._issue_warning("assertTrue")
+        return super().assertTrue(*args, **kwargs)
+
+    def assertFalse(self, *args, **kwargs):
+        self._issue_warning("assertFalse")
+        return super().assertFalse(*args, **kwargs)
+
+    def assertIsNone(self, *args, **kwargs):
+        self._issue_warning("assertIsNone")
+        return super().assertIsNone(*args, **kwargs)
+
+    def assertIsNotNone(self, *args, **kwargs):
+        self._issue_warning("assertIsNotNone")
+        return super().assertIsNotNone(*args, **kwargs)
+
+    def assertIn(self, *args, **kwargs):  # codespell:ignore
+        self._issue_warning("assertIn")  # codespell:ignore
+        return super().assertIn(*args, **kwargs)  # codespell:ignore
+
+    def assertNotIn(self, *args, **kwargs):
+        self._issue_warning("assertNotIn")
+        return super().assertNotIn(*args, **kwargs)
+
+    def assertIsInstance(self, *args, **kwargs):
+        self._issue_warning("assertIsInstance")
+        return super().assertIsInstance(*args, **kwargs)
+
+    def assertNotIsInstance(self, *args, **kwargs):
+        self._issue_warning("assertNotIsInstance")
+        return super().assertNotIsInstance(*args, **kwargs)
+
+    def assertRaises(self, *args, **kwargs):
+        self._issue_warning("assertRaises")
+        return super().assertRaises(*args, **kwargs)