More BaseValidationErrors tests

src/cattrs/errors.py

@@ -1,5 +1,8 @@
+from collections.abc import Sequence
 from typing import Any, Optional, Union
 
+from typing_extensions import Self
+
 from cattrs._compat import ExceptionGroup
 
 
@@ -17,13 +20,13 @@ def __init__(self, message: str, type_: type) -> None:
 class BaseValidationError(ExceptionGroup):
     cl: type
 
-    def __new__(cls, message, excs, cl: type):
+    def __new__(cls, message: str, excs: Sequence[Exception], cl: type):
         obj = super().__new__(cls, message, excs)
         obj.cl = cl
         return obj
 
-    def derive(self, excs):
-        return ClassValidationError(self.message, excs, self.cl)
+    def derive(self, excs: Sequence[Exception]) -> Self:
+        return self.__class__(self.message, excs, self.cl)
 
 
 class IterableValidationNote(str):

tests/test_validation.py

@@ -222,3 +222,25 @@ def test_notes_pickling():
     assert note == "foo"
     assert note.name == "name"
     assert note.type is int
+
+
+def test_error_derive():
+    """Our ExceptionGroups should derive properly."""
+    c = Converter(detailed_validation=True)
+
+    @define
+    class Test:
+        a: int
+        b: str = field(validator=in_(["a", "b"]))
+        c: str
+
+    with pytest.raises(ClassValidationError) as exc:
+        c.structure({"a": "a", "b": "c"}, Test)
+
+    match, rest = exc.value.split(KeyError)
+
+    assert len(match.exceptions) == 1
+    assert len(rest.exceptions) == 1
+
+    assert match.cl == exc.value.cl
+    assert rest.cl == exc.value.cl