feat: 10865

changelog/10865.bugfix.rst

@@ -0,0 +1 @@
+Fix a TypeError in a warning arguments call muted by warnings filter.

src/_pytest/recwarn.py

@@ -329,3 +329,11 @@ class WarningsChecker(WarningsRecorder):
                         module=w.__module__,
                         source=w.source,
                     )
+            # Check warnings has valid argument type
+            wrn: warnings.WarningMessage
+            for wrn in self:
+                if isinstance(wrn.message, Warning):
+                    if not isinstance(wrn.message.args[0], str):
+                        raise TypeError(
+                            f"Warning message must be str, got {type(wrn.message.args[0])}"
+                        )

testing/python/test_warning_attributes.py

@@ -0,0 +1,17 @@
+from _pytest.pytester import Pytester
+
+
+class TestWarningAttributes:
+    def test_raise_type_error(self, pytester: Pytester) -> None:
+        pytester.makepyfile(
+            """
+            import pytest
+            import warnings
+
+            def test_example_one():
+                with pytest.warns(UserWarning):
+                    warnings.warn(1)
+            """
+        )
+        result = pytester.runpytest()
+        result.stdout.fnmatch_lines(["*1 failed*"])