From 9dae6bc70bcd241482a83cbc8c2271463dbbca25 Mon Sep 17 00:00:00 2001
From: yucheng-berri <293926326+yucheng-berri@users.noreply.github.com>
Date: Fri, 30 Oct 2026 12:56:00 -0700
Subject: [PATCH] test(streaming): a merged reasoning stream cut mid reasoning
 now fails

Main's think tag test expected a stream that ends mid reasoning without a finish reason to finish with a closed think block. With this PR that stream fails, so the case moves to its own test that expects MidStreamFallbackError with the open think block as the partial content
---
 .../test_streaming_handler.py                 | 26 ++++++++++++++-----
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/tests/unit/litellm_core_utils/test_streaming_handler.py b/tests/unit/litellm_core_utils/test_streaming_handler.py
index ca5f9c5a63f..e3201263a3c 100644
--- a/tests/unit/litellm_core_utils/test_streaming_handler.py
+++ b/tests/unit/litellm_core_utils/test_streaming_handler.py
@@ -576,11 +576,6 @@ _GET_WEATHER_CALL: Final = {
             "<think>a</think>b<think>c</think>d",
             0,
         ),
-        (
-            (_stream_chunk({"reasoning_content": "Still thinking"}),),
-            "<think>Still thinking</think>",
-            0,
-        ),
         (
             (_stream_chunk({"content": "hi"}), _stream_chunk({}, "stop")),
             "hi",
@@ -592,7 +587,6 @@ _GET_WEATHER_CALL: Final = {
         "reasoning_then_function_call",
         "reasoning_cut_by_length",
         "reasoning_after_answer",
-        "stream_ends_mid_reasoning",
         "answer_without_reasoning",
     ],
 )
@@ -626,6 +620,26 @@ async def test_merged_reasoning_stream_keeps_think_tags_balanced(
     )
 
 
+@pytest.mark.asyncio
+@pytest.mark.parametrize("sync_mode", [True, False])
+async def test_merged_reasoning_stream_cut_mid_reasoning_fails_instead_of_closing_the_think_block(
+    logging_obj: Logging, sync_mode: bool
+) -> None:
+    response: Final = CustomStreamWrapper(
+        completion_stream=ModelResponseListIterator(
+            model_responses=[_stream_chunk({"reasoning_content": "Still thinking"})]
+        ),
+        model="deepseek-reasoner",
+        logging_obj=logging_obj,
+    )
+    response.merge_reasoning_content_in_choices = True
+
+    with pytest.raises(MidStreamFallbackError) as excinfo:
+        await _collect(response, sync_mode)
+
+    assert excinfo.value.generated_content == "<think>Still thinking"
+
+
 def test_strip_sse_data_from_chunk():
     """Test the static method that strips 'data: ' prefix from SSE chunks"""
     # Test with string inputs