json mode standard test (#25497)

Co-authored-by: Chester Curme <chester.curme@gmail.com>

libs/standard-tests/langchain_tests/unit_tests/chat_models.py

@@ -132,6 +132,11 @@ class ChatModelTests(BaseStandardTests):
             is not BaseChatModel.with_structured_output
         )
 
+    @property
+    def supports_json_mode(self) -> bool:
+        """(bool) whether the chat model supports JSON mode."""
+        return False
+
     @property
     def supports_image_inputs(self) -> bool:
         """(bool) whether the chat model supports image inputs, defaults to
@@ -281,7 +286,7 @@ class ChatModelUnitTests(ChatModelTests):
         output.
 
         By default, this is determined by whether the chat model's
-        `with_structured_output` method is overridden. If the base implementation is
+        ``with_structured_output`` method is overridden. If the base implementation is
         intended to be used, this method should be overridden.
 
         See: https://python.langchain.com/docs/concepts/structured_outputs/
@@ -294,6 +299,21 @@ class ChatModelUnitTests(ChatModelTests):
             def has_structured_output(self) -> bool:
                 return True
 
+    .. dropdown:: supports_json_mode
+
+        Boolean property indicating whether the chat model supports JSON mode in
+        ``with_structured_output``.
+
+        See: https://python.langchain.com/docs/concepts/structured_outputs/#json-mode
+
+        Example:
+
+        .. code-block:: python
+
+            @property
+            def supports_json_mode(self) -> bool:
+                return True
+
     .. dropdown:: supports_image_inputs
 
         Boolean property indicating whether the chat model supports image inputs.