fix test_json_response_format

tests/llm_translation/base_llm_unit_tests.py

@@ -82,6 +82,10 @@ class BaseLLMChatTest(ABC):
 
         print(response)
 
+        # OpenAI guarantees that the JSON schema is returned in the content
+        # relevant issue: https://github.com/BerriAI/litellm/issues/6741
+        assert response.choices[0].message.content is not None
+
     @pytest.fixture
     def pdf_messages(self):
         import base64