fix: address review comments on MRO marker iteration

- Add @OverRide decorator to Class._iter_own_markers_closest_first
  (with version-gated import for Python <3.12)
- Broaden isinstance check from list to Sequence for cls_marks
- Add test for dynamically added markers on Class collectors

Co-authored-by: Cursor AI <ai@cursor.sh>
Co-authored-by: Anthropic Claude Opus 4.6 <claude@anthropic.com>

Author: 3 people

src/_pytest/python.py

@@ -21,6 +21,7 @@
 import os
 from pathlib import Path
 import re
+import sys
 import textwrap
 import types
 from typing import Any
@@ -79,6 +80,14 @@
 from _pytest.warning_types import PytestReturnNotNoneWarning
 
 
+if sys.version_info >= (3, 12):
+    from typing import override
+else:
+
+    def override(func):
+        return func
+
+
 if TYPE_CHECKING:
     from typing_extensions import Self
 
@@ -751,6 +760,7 @@ def from_parent(cls, parent, *, name, obj=None, **kw) -> Self:  # type: ignore[o
         """The public constructor."""
         return super().from_parent(name=name, parent=parent, **kw)
 
+    @override
     def _iter_own_markers_closest_first(self) -> Iterator[Mark]:
         """own_markers stores MRO markers in base-first order
         (construction order). For closest-first iteration, reverse at the
@@ -763,7 +773,7 @@ def _iter_own_markers_closest_first(self) -> Iterator[Mark]:
         mro_mark_ids: set[int] = set()
         for cls in self.obj.__mro__:
             cls_marks = cls.__dict__.get("pytestmark", [])
-            if not isinstance(cls_marks, list):
+            if not isinstance(cls_marks, Sequence):
                 cls_marks = [cls_marks]
             for mark in normalize_mark_list(cls_marks):
                 mro_mark_ids.add(id(mark))

testing/test_mark.py

@@ -690,6 +690,40 @@ def test_function_and_class(self, request):
         result = pytester.runpytest()
         result.assert_outcomes(passed=4)
 
+    def test_mark_closest_mro_with_dynamic_class_marker(
+        self, pytester: Pytester
+    ) -> None:
+        """Dynamic markers added to a Class collector via add_marker appear
+        alongside MRO markers in iter_markers (#14329)."""
+        pytester.makeconftest(
+            """
+            import pytest
+
+            def pytest_collectstart(collector):
+                if getattr(collector, "name", None) == "TestChild":
+                    collector.add_marker(pytest.mark.foo(99))
+            """
+        )
+        pytester.makepyfile(
+            """
+            import pytest
+
+            @pytest.mark.foo(0)
+            class TestBase:
+                pass
+
+            @pytest.mark.foo(1)
+            class TestChild(TestBase):
+                def test_it(self, request):
+                    names = [m.args[0] for m in request.node.iter_markers("foo")]
+                    # MRO markers (child=1, base=0) plus dynamic marker (99)
+                    assert 99 in names
+                    assert names.index(1) < names.index(0)
+            """
+        )
+        result = pytester.runpytest()
+        result.assert_outcomes(passed=1)
+
     def test_mark_with_wrong_marker(self, pytester: Pytester) -> None:
         reprec = pytester.inline_runsource(
             """