test(podcasts): cover renderer validation

surfsense_backend/tests/unit/podcasts/test_renderer.py

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+"""The renderer refuses an inconsistent spec/transcript before spending work.
+
+Full synthesis-and-merge needs FFmpeg and a real provider, so it belongs to an
+integration test. What is pure and worth securing here is the renderer's
+contract that it validates the transcript against the brief up front: a turn
+naming an unknown speaker, or a speaker naming an unknown voice, fails loudly
+rather than producing silent or wrong audio. The TTS provider is an external
+port, faked here and never expected to be called on these paths.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+from app.podcasts.rendering import PodcastRenderer, RenderError
+from app.podcasts.schemas import (
+    DurationTarget,
+    PodcastSpec,
+    SpeakerRole,
+    SpeakerSpec,
+    Transcript,
+    TranscriptTurn,
+)
+from app.podcasts.tts import SynthesizedAudio
+from app.podcasts.voices import CatalogVoice, TtsProvider, VoiceCatalog, VoiceGender
+
+pytestmark = pytest.mark.unit
+
+
+class _UnusedTTS:
+    """A TTS port double that fails the test if it is ever asked to speak.
+
+    These behaviors must short-circuit before synthesis, so any call here is a
+    regression.
+    """
+
+    @property
+    def container(self) -> str:
+        return "mp3"
+
+    async def synthesize(self, _request):  # pragma: no cover - must not run
+        raise AssertionError("synthesis should not be attempted")
+        return SynthesizedAudio(data=b"", container="mp3")
+
+
+def _catalog_with(voice_id: str) -> VoiceCatalog:
+    return VoiceCatalog(
+        [
+            CatalogVoice(
+                voice_id=voice_id,
+                provider=TtsProvider.KOKORO,
+                language="en-US",
+                display_name=voice_id,
+                gender=VoiceGender.MALE,
+                native_ref="am_adam",
+            )
+        ]
+    )
+
+
+def _spec(voice_id: str) -> PodcastSpec:
+    return PodcastSpec(
+        language="en",
+        speakers=[
+            SpeakerSpec(slot=0, name="Host", role=SpeakerRole.HOST, voice_id=voice_id)
+        ],
+        duration=DurationTarget(min_minutes=5, max_minutes=10),
+    )
+
+
+async def test_render_rejects_a_turn_for_an_unknown_speaker(tmp_path):
+    renderer = PodcastRenderer(tts=_UnusedTTS(), catalog=_catalog_with("kokoro:am_adam"))
+    transcript = Transcript(turns=[TranscriptTurn(speaker=5, text="Who am I?")])
+
+    with pytest.raises(RenderError):
+        await renderer.render(
+            spec=_spec("kokoro:am_adam"), transcript=transcript, workdir=Path(tmp_path)
+        )
+
+
+async def test_render_rejects_a_speaker_whose_voice_is_not_in_the_catalog(tmp_path):
+    renderer = PodcastRenderer(tts=_UnusedTTS(), catalog=_catalog_with("kokoro:am_adam"))
+    transcript = Transcript(turns=[TranscriptTurn(speaker=0, text="Hello.")])
+
+    with pytest.raises(RenderError):
+        await renderer.render(
+            spec=_spec("kokoro:ghost"), transcript=transcript, workdir=Path(tmp_path)
+        )