Clean up type hints and add a test (#13348)

Based on discussion in #13345.

Author: rouge8

src/_pytest/reports.py

@@ -261,8 +261,6 @@ class TestReport(BaseReport):
 
     __test__ = False
 
-    when: Literal["setup", "call", "teardown"]
-    location: tuple[str, int | None, str]
     # Defined by skipping plugin.
     # xfail reason if xfailed, otherwise not defined. Use hasattr to distinguish.
     wasxfail: str
@@ -307,7 +305,7 @@ def __init__(
         self.longrepr = longrepr
 
         #: One of 'setup', 'call', 'teardown' to indicate runtest phase.
-        self.when = when
+        self.when: Literal["setup", "call", "teardown"] = when
 
         #: User properties is a list of tuples (name, value) that holds user
         #: defined properties of the test.

testing/typing_checks.py

@@ -8,12 +8,14 @@
 from __future__ import annotations
 
 import contextlib
+from typing import Literal
 from typing import Optional
 
 from typing_extensions import assert_type
 
 import pytest
 from pytest import MonkeyPatch
+from pytest import TestReport
 
 
 # Issue #7488.
@@ -51,3 +53,9 @@ def check_raises_is_a_context_manager(val: bool) -> None:
     with pytest.raises(RuntimeError) if val else contextlib.nullcontext() as excinfo:
         pass
     assert_type(excinfo, Optional[pytest.ExceptionInfo[RuntimeError]])
+
+
+# Issue #12941.
+def check_testreport_attributes(report: TestReport) -> None:
+    assert_type(report.when, Literal["setup", "call", "teardown"])
+    assert_type(report.location, tuple[str, Optional[int], str])