Merge pull request #8677 from olgarithms/warns-no-arg-catches-any

AUTHORS

@@ -231,6 +231,7 @@ Nicholas Murphy
 Niclas Olofsson
 Nicolas Delaby
 Nikolay Kondratyev
+Olga Matoula
 Oleg Pidsadnyi
 Oleg Sushchenko
 Oliver Bestwalter

changelog/8645.improvement.rst

@@ -0,0 +1,4 @@
+Reducing confusion from `pytest.warns(None)` by:
+
+- Allowing no arguments to be passed in order to catch any exception (no argument defaults to `Warning`).
+- Emit a deprecation warning if passed `None`.

doc/en/how-to/capture-warnings.rst

@@ -332,11 +332,11 @@ You can record raised warnings either using func:`pytest.warns` or with
 the ``recwarn`` fixture.
 
 To record with func:`pytest.warns` without asserting anything about the warnings,
-pass ``None`` as the expected warning type:
+pass no arguments as the expected warning type and it will default to a generic Warning:
 
 .. code-block:: python
 
-    with pytest.warns(None) as record:
+    with pytest.warns() as record:
         warnings.warn("user", UserWarning)
         warnings.warn("runtime", RuntimeWarning)
 

src/_pytest/deprecated.py

@@ -101,6 +101,12 @@ HOOK_LEGACY_PATH_ARG = UnformattedWarning(
     "see https://docs.pytest.org/en/latest/deprecations.html"
     "#py-path-local-arguments-for-hooks-replaced-with-pathlib-path",
 )
+
+WARNS_NONE_ARG = PytestDeprecationWarning(
+    "Passing None to catch any warning has been deprecated, pass no arguments instead:\n"
+    " Replace pytest.warns(None) by simply pytest.warns()."
+)
+
 # You want to make some `__init__` or function "private".
 #
 #   def my_private_function(some, args):

src/_pytest/recwarn.py

@@ -17,6 +17,7 @@ from typing import Union
 
 from _pytest.compat import final
 from _pytest.deprecated import check_ispytest
+from _pytest.deprecated import WARNS_NONE_ARG
 from _pytest.fixtures import fixture
 from _pytest.outcomes import fail
 
@@ -83,7 +84,7 @@ def deprecated_call(
 
 @overload
 def warns(
-    expected_warning: Optional[Union[Type[Warning], Tuple[Type[Warning], ...]]],
+    expected_warning: Union[Type[Warning], Tuple[Type[Warning], ...]] = ...,
     *,
     match: Optional[Union[str, Pattern[str]]] = ...,
 ) -> "WarningsChecker":
@@ -92,7 +93,7 @@ def warns(
 
 @overload
 def warns(
-    expected_warning: Optional[Union[Type[Warning], Tuple[Type[Warning], ...]]],
+    expected_warning: Union[Type[Warning], Tuple[Type[Warning], ...]],
     func: Callable[..., T],
     *args: Any,
     **kwargs: Any,
@@ -101,7 +102,7 @@ def warns(
 
 
 def warns(
-    expected_warning: Optional[Union[Type[Warning], Tuple[Type[Warning], ...]]],
+    expected_warning: Union[Type[Warning], Tuple[Type[Warning], ...]] = Warning,
     *args: Any,
     match: Optional[Union[str, Pattern[str]]] = None,
     **kwargs: Any,
@@ -232,7 +233,7 @@ class WarningsChecker(WarningsRecorder):
         self,
         expected_warning: Optional[
             Union[Type[Warning], Tuple[Type[Warning], ...]]
-        ] = None,
+        ] = Warning,
         match_expr: Optional[Union[str, Pattern[str]]] = None,
         *,
         _ispytest: bool = False,
@@ -242,6 +243,7 @@ class WarningsChecker(WarningsRecorder):
 
         msg = "exceptions must be derived from Warning, not %s"
         if expected_warning is None:
+            warnings.warn(WARNS_NONE_ARG, stacklevel=4)
             expected_warning_tup = None
         elif isinstance(expected_warning, tuple):
             for exc in expected_warning:

testing/deprecated_test.py

@@ -178,3 +178,15 @@ def test_hookproxy_warnings_for_fspath(tmp_path, hooktype, request):
     assert l1 < record.lineno < l2
 
     hooks.pytest_ignore_collect(config=request.config, fspath=tmp_path)
+
+
+def test_warns_none_is_deprecated():
+    with pytest.warns(
+        PytestDeprecationWarning,
+        match=re.escape(
+            "Passing None to catch any warning has been deprecated, pass no arguments instead:\n "
+            "Replace pytest.warns(None) by simply pytest.warns()."
+        ),
+    ):
+        with pytest.warns(None):  # type: ignore[call-overload]
+            pass

testing/test_recwarn.py

@@ -298,7 +298,7 @@ class TestWarns:
         assert str(record[0].message) == "user"
 
     def test_record_only(self) -> None:
-        with pytest.warns(None) as record:
+        with pytest.warns() as record:
             warnings.warn("user", UserWarning)
             warnings.warn("runtime", RuntimeWarning)
 
@@ -306,6 +306,18 @@ class TestWarns:
         assert str(record[0].message) == "user"
         assert str(record[1].message) == "runtime"
 
+    def test_record_only_none_deprecated_warn(self) -> None:
+        # This should become an error when WARNS_NONE_ARG is removed in Pytest 7.0
+        with warnings.catch_warnings():
+            warnings.simplefilter("ignore")
+            with pytest.warns(None) as record:  # type: ignore[call-overload]
+                warnings.warn("user", UserWarning)
+                warnings.warn("runtime", RuntimeWarning)
+
+            assert len(record) == 2
+            assert str(record[0].message) == "user"
+            assert str(record[1].message) == "runtime"
+
     def test_record_by_subclass(self) -> None:
         with pytest.warns(Warning) as record:
             warnings.warn("user", UserWarning)

testing/test_tmpdir.py

@@ -1,6 +1,7 @@
 import os
 import stat
 import sys
+import warnings
 from pathlib import Path
 from typing import Callable
 from typing import cast
@@ -400,11 +401,13 @@ class TestRmRf:
             assert fn.is_file()
 
         # ignored function
-        with pytest.warns(None) as warninfo:
-            exc_info4 = (None, PermissionError(), None)
-            on_rm_rf_error(os.open, str(fn), exc_info4, start_path=tmp_path)
-            assert fn.is_file()
-        assert not [x.message for x in warninfo]
+        with warnings.catch_warnings():
+            warnings.simplefilter("ignore")
+            with pytest.warns(None) as warninfo:  # type: ignore[call-overload]
+                exc_info4 = (None, PermissionError(), None)
+                on_rm_rf_error(os.open, str(fn), exc_info4, start_path=tmp_path)
+                assert fn.is_file()
+            assert not [x.message for x in warninfo]
 
         exc_info5 = (None, PermissionError(), None)
         on_rm_rf_error(os.unlink, str(fn), exc_info5, start_path=tmp_path)