test(openai): add openai unit test for streaming error in _generate method

- Add test for streaming error with multiple prompts

Author: Ali-Ismail-1

libs/partners/openai/tests/unit_tests/llms/test_base.py

@@ -108,3 +108,13 @@ def test_stream_response_to_generation_chunk() -> None:
     assert chunk == GenerationChunk(
         text="", generation_info={"finish_reason": None, "logprobs": None}
     )
+
+
+def test_generate_streaming_multiple_prompts_error() -> None:
+    """Ensures ValueError when streaming=True and multiple prompts."""
+    llm = OpenAI(streaming=True)
+
+    with pytest.raises(
+        ValueError, match="Cannot stream results with multiple prompts\\."
+    ):
+        llm._generate(["foo", "bar"])