fix doctest and improve unit tests

Author: aaronzo

src/_pytest/recwarn.py

@@ -145,15 +145,15 @@ def warns(
     You may also set the keyword argument ``keep_ignores`` to avoid catching warnings
     which were filtered out, in pytest configuration or otherwise::
 
-        >>> warnings.simplefilter("ignore", category=FutureWarning)
+        >>> warnings.simplefilter("ignore", category=UserWarning)
         >>> with pytest.warns(UserWarning, keep_ignores=True):
         ...     warnings.warn("ignore this warning", UserWarning)
         Traceback (most recent call last):
           ...
         Failed: DID NOT WARN. No warnings of type ...UserWarning... were emitted...
 
         >>> with pytest.warns(RuntimeWarning):
-        >>>     warnings.simplefilter("ignore", category=FutureWarning)
+        >>>     warnings.simplefilter("ignore", category=UserWarning)
         >>>     with pytest.warns(UserWarning, keep_ignores=True):
         ...         warnings.warn("ignore this warning", UserWarning)
                     warnings.warn("keep this warning", RuntimeWarning)
@@ -260,13 +260,15 @@ def __enter__(self) -> Self:
 
         if self._keep_ignores:
             for action, message, category, module, lineno in reversed(warnings.filters):
+                if isinstance(message, re.Pattern):
+                    module = getattr(module, "pattern", None)  # type: ignore[unreachable]
                 if isinstance(module, re.Pattern):
                     module = getattr(module, "pattern", None)  # type: ignore[unreachable]
                 warnings.filterwarnings(
                     action="always" if action != "ignore" else "ignore",
-                    message=message if isinstance(message, str) else "",
+                    message=message or "",
                     category=category,
-                    module=module if isinstance(module, str) else "",
+                    module=module or "",
                     lineno=lineno,
                 )
         else:

testing/test_recwarn.py

@@ -416,6 +416,12 @@ def test_keep_ignores(self) -> None:
                 with pytest.warns(UserWarning, keep_ignores=True):
                     warnings.warn("ignore this warning", FutureWarning)
 
+        with pytest.raises(pytest.fail.Exception, match="DID NOT WARN"):
+            with warnings.catch_warnings():
+                warnings.filterwarnings("ignore", message="ignore this")
+                with pytest.warns(UserWarning, keep_ignores=True):
+                    warnings.warn("ignore this warning", UserWarning)
+
     def test_one_from_multiple_warns(self) -> None:
         with pytest.warns():
             with pytest.raises(pytest.fail.Exception, match="DID NOT WARN"):