diff --git a/src/_pytest/recwarn.py b/src/_pytest/recwarn.py
index 5d2a98b2c..62df274bd 100644
--- a/src/_pytest/recwarn.py
+++ b/src/_pytest/recwarn.py
@@ -332,8 +332,11 @@ class WarningsChecker(WarningsRecorder):
             # Check warnings has valid argument type (#10865).
             wrn: warnings.WarningMessage
             for wrn in self:
-                if isinstance(wrn.message, Warning):
-                    if not isinstance(msg := wrn.message.args[0], str):
-                        raise TypeError(
-                            f"Warning message must be str, got {msg!r} (type {type(msg).__name__})"
-                        )
+                self._validate_message(wrn)
+
+    @staticmethod
+    def _validate_message(wrn: Any) -> None:
+        if not isinstance(msg := wrn.message.args[0], str):
+            raise TypeError(
+                f"Warning message must be str, got {msg!r} (type {type(msg).__name__})"
+            )