test(elevenlabs): cover multichannel transcription request/response transforms

- request: boolean form values (use_multi_channel/diarize) serialize lowercase
- response: per-channel transcripts[] + audio_duration_secs are surfaced
- response: single-channel responses keep the flat text (back-compat)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_litellm/llms/elevenlabs/audio_transcription/test_elevenlabs_audio_transcription_transformation.py

@@ -0,0 +1,77 @@
+import json
+
+import httpx
+
+from litellm.llms.base_llm.audio_transcription.transformation import (
+    AudioTranscriptionRequestData,
+)
+from litellm.llms.elevenlabs.audio_transcription.transformation import (
+    ElevenLabsAudioTranscriptionConfig,
+)
+
+
+def _response(payload: dict) -> httpx.Response:
+    return httpx.Response(
+        200,
+        content=json.dumps(payload).encode(),
+        request=httpx.Request("POST", "https://api.elevenlabs.io/v1/speech-to-text"),
+    )
+
+
+def test_request_serializes_bool_form_values_lowercase():
+    """Boolean optional params must reach ElevenLabs as lowercase ``true``/``false``
+    (httpx-style), not Python's ``str(True)`` -> ``"True"``; otherwise flags such as
+    ``use_multi_channel`` / ``diarize`` are silently ignored."""
+    config = ElevenLabsAudioTranscriptionConfig()
+
+    result = config.transform_audio_transcription_request(
+        model="scribe_v2",
+        audio_file=b"\x00\x01\x02\x03",
+        optional_params={"use_multi_channel": True, "diarize": False},
+        litellm_params={},
+    )
+
+    assert isinstance(result, AudioTranscriptionRequestData)
+    assert result.data["model_id"] == "scribe_v2"
+    assert result.data["use_multi_channel"] == "true"
+    assert result.data["diarize"] == "false"
+
+
+def test_response_preserves_multichannel_transcripts():
+    """A ``use_multi_channel`` response carries a per-channel ``transcripts`` array;
+    it must survive on the TranscriptionResponse (along with ``audio_duration_secs``)
+    rather than being flattened to a single ``text``."""
+    config = ElevenLabsAudioTranscriptionConfig()
+
+    payload = {
+        "transcripts": [
+            {
+                "channel_index": 0,
+                "words": [{"text": "hello", "start": 0.0, "end": 0.4, "type": "word"}],
+            },
+            {
+                "channel_index": 1,
+                "words": [{"text": "hi", "start": 0.2, "end": 0.5, "type": "word"}],
+            },
+        ],
+        "audio_duration_secs": 1.5,
+        "language_code": "en",
+    }
+
+    response = config.transform_audio_transcription_response(_response(payload))
+
+    assert [t["channel_index"] for t in response["transcripts"]] == [0, 1]
+    assert response["transcripts"][0]["words"][0]["text"] == "hello"
+    assert response["audio_duration_secs"] == 1.5
+
+
+def test_response_single_channel_is_unchanged():
+    """Single-channel responses keep the flat ``text`` and gain no ``transcripts`` key."""
+    config = ElevenLabsAudioTranscriptionConfig()
+
+    response = config.transform_audio_transcription_response(
+        _response({"text": "hello world", "language_code": "en"})
+    )
+
+    assert response.text == "hello world"
+    assert "transcripts" not in response.model_dump()