add ProviderMetaclass test

packages/jupyter-ai-magics/jupyter_ai_magics/tests/test_provider_metaclass.py

@@ -0,0 +1,25 @@
+from typing import ClassVar, Optional
+from ..providers import ProviderMetaclass
+from langchain.pydantic_v1 import BaseModel
+
+
+def test_provider_metaclass():
+    """
+    Asserts that the metaclass prevents class attributes from being omitted due
+    to parent classes defining an instance field of the same name.
+
+    You can reproduce the original issue by removing the
+    `metaclass=ProviderMetaclass` argument from the definition of `Child`.
+    """
+
+    class Parent(BaseModel):
+        test: Optional[str]
+
+    class Base(BaseModel):
+        test: ClassVar[str]
+
+    class Child(Base, Parent, metaclass=ProviderMetaclass):
+        test: ClassVar[str] = "expected"
+
+    assert Child.test == "expected"
+