Fix type failures in raises.py and add tests

Fix typing failures after mypy 1.18 update.

Author: jakkdl

src/_pytest/raises.py

@@ -452,7 +452,7 @@ def _parse_exc(
                 issubclass(origin_exc, BaseExceptionGroup)
                 and exc_type in (BaseException, Any)
             ):
-                if not isinstance(exc, Exception):
+                if not issubclass(origin_exc, ExceptionGroup):
                     self.is_baseexception = True
                 return cast(type[BaseExcT_1], origin_exc)
             else:
@@ -465,9 +465,9 @@ def _parse_exc(
                 )
         # unclear if the Type/ValueError distinction is even helpful here
         msg = f"expected exception must be {expected}, not "
-        if isinstance(exc, type):
+        if isinstance(exc, type):  # type: ignore[unreachable]
             raise ValueError(msg + f"{exc.__name__!r}")
-        if isinstance(exc, BaseException):
+        if isinstance(exc, BaseException):  # type: ignore[unreachable]
             raise TypeError(msg + f"an exception instance ({type(exc).__name__})")
         raise TypeError(msg + repr(type(exc).__name__))
 

testing/python/raises_group.py

@@ -1325,6 +1325,16 @@ def test_annotated_group() -> None:
     with RaisesExc(BaseExceptionGroup[BaseException]):
         raise BaseExceptionGroup("", [KeyboardInterrupt()])
 
+    # assure AbstractRaises.is_baseexception is set properly
+    assert (
+        RaisesGroup(ExceptionGroup[Exception]).expected_type()
+        == "ExceptionGroup(ExceptionGroup)"
+    )
+    assert (
+        RaisesGroup(BaseExceptionGroup[BaseException]).expected_type()
+        == "BaseExceptionGroup(BaseExceptionGroup)"
+    )
+
 
 def test_tuples() -> None:
     # raises has historically supported one of several exceptions being raised

testing/test_monkeypatch.py

@@ -417,7 +417,7 @@ def test_context() -> None:
     with monkeypatch.context() as m:
         m.setattr(functools, "partial", 3)
         assert not inspect.isclass(functools.partial)
-    assert inspect.isclass(functools.partial)  # type:ignore[unreachable]
+    assert inspect.isclass(functools.partial)
 
 
 def test_context_classmethod() -> None: