standard-tests: Add BaseModel variations tests to with_structured_output (#24527)

After this standard tests will test with the following combinations:

1. pydantic.BaseModel
2. pydantic.v1.BaseModel

If ran within a matrix, it'll covert both pydantic.BaseModel originating
from
pydantic 1 and the one defined in pydantic 2.

libs/standard-tests/langchain_standard_tests/integration_tests/chat_models.py

@@ -23,6 +23,7 @@ from langchain_standard_tests.unit_tests.chat_models import (
     ChatModelTests,
     my_adder_tool,
 )
+from langchain_standard_tests.utils.pydantic import PYDANTIC_MAJOR_VERSION
 
 
 @tool
@@ -211,10 +212,51 @@ class ChatModelIntegrationTests(ChatModelTests):
         assert tool_call["type"] == "tool_call"
 
     def test_structured_output(self, model: BaseChatModel) -> None:
+        """Test to verify structured output with a Pydantic model."""
         if not self.has_tool_calling:
             pytest.skip("Test requires tool calling.")
 
-        class Joke(BaseModel):
+        from pydantic import BaseModel as BaseModelProper
+        from pydantic import Field as FieldProper
+
+        class Joke(BaseModelProper):
+            """Joke to tell user."""
+
+            setup: str = FieldProper(description="question to set up a joke")
+            punchline: str = FieldProper(description="answer to resolve the joke")
+
+        # Pydantic class
+        # Type ignoring since the interface only officially supports pydantic 1
+        # or pydantic.v1.BaseModel but not pydantic.BaseModel from pydantic 2.
+        # We'll need to do a pass updating the type signatures.
+        chat = model.with_structured_output(Joke)  # type: ignore[arg-type]
+        result = chat.invoke("Tell me a joke about cats.")
+        assert isinstance(result, Joke)
+
+        for chunk in chat.stream("Tell me a joke about cats."):
+            assert isinstance(chunk, Joke)
+
+        # Schema
+        chat = model.with_structured_output(Joke.schema())
+        result = chat.invoke("Tell me a joke about cats.")
+        assert isinstance(result, dict)
+        assert set(result.keys()) == {"setup", "punchline"}
+
+        for chunk in chat.stream("Tell me a joke about cats."):
+            assert isinstance(chunk, dict)
+        assert isinstance(chunk, dict)  # for mypy
+        assert set(chunk.keys()) == {"setup", "punchline"}
+
+    @pytest.mark.skipif(PYDANTIC_MAJOR_VERSION != 2, "Test requires pydantic 2.")
+    def test_structured_output_pydantic_2_v1(self, model: BaseChatModel) -> None:
+        """Test to verify compatibility with pydantic.v1.BaseModel.
+
+        pydantic.v1.BaseModel is available in the pydantic 2 package.
+        """
+        if not self.has_tool_calling:
+            pytest.skip("Test requires tool calling.")
+
+        class Joke(BaseModel):  # Uses langchain_core.pydantic_v1.BaseModel
             """Joke to tell user."""
 
             setup: str = Field(description="question to set up a joke")