test(podcasts): cover language and voice resolution

surfsense_backend/tests/unit/podcasts/test_resolution.py

@@ -0,0 +1,100 @@
+"""Default language and voice selection for a fresh brief.
+
+Resolution is what lets most briefs need no edits: it proposes a sensible
+language and a distinct voice per speaker. These tests state the policy
+("detected wins, else last-used, else English"; "two speakers should sound
+like two people") through the public resolver functions and the real catalog.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from app.podcasts.resolution import (
+    DEFAULT_LANGUAGE,
+    LanguageContext,
+    VoiceResolutionError,
+    resolve_language,
+    resolve_voices,
+)
+from app.podcasts.voices import TtsProvider, get_voice_catalog
+
+pytestmark = pytest.mark.unit
+
+
+def test_detected_language_is_preferred_over_everything():
+    context = LanguageContext(detected="es", last_used="fr")
+    assert resolve_language(context) == "es"
+
+
+def test_falls_back_to_last_used_when_nothing_detected():
+    context = LanguageContext(detected=None, last_used="fr")
+    assert resolve_language(context) == "fr"
+
+
+def test_first_time_user_with_no_signal_gets_the_default():
+    assert resolve_language(LanguageContext()) == DEFAULT_LANGUAGE
+
+
+def test_two_speakers_get_distinct_voices():
+    """A two-speaker episode should not voice both with the same person."""
+    catalog = get_voice_catalog()
+    voices = resolve_voices(
+        catalog=catalog, provider=TtsProvider.KOKORO, language="en", speaker_count=2
+    )
+    assert len(voices) == 2
+    assert voices[0].voice_id != voices[1].voice_id
+
+
+def test_a_users_preferred_voice_is_reused_when_still_valid():
+    catalog = get_voice_catalog()
+    voices = resolve_voices(
+        catalog=catalog,
+        provider=TtsProvider.KOKORO,
+        language="en",
+        speaker_count=2,
+        preferred=["kokoro:af_bella"],
+    )
+    assert voices[0].voice_id == "kokoro:af_bella"
+
+
+def test_a_preferred_voice_invalid_for_the_language_is_replaced():
+    """A stale preference (wrong provider/language) is silently dropped."""
+    catalog = get_voice_catalog()
+    voices = resolve_voices(
+        catalog=catalog,
+        provider=TtsProvider.KOKORO,
+        language="en",
+        speaker_count=1,
+        preferred=["kokoro:does-not-exist"],
+    )
+    assert voices[0].voice_id in {v.voice_id for v in catalog.for_provider(TtsProvider.KOKORO)}
+
+
+def test_resolution_fails_when_no_voice_speaks_the_language():
+    """If a provider can't speak the language at all, that is surfaced loudly."""
+    catalog = get_voice_catalog()
+    with pytest.raises(VoiceResolutionError):
+        resolve_voices(
+            catalog=catalog,
+            provider=TtsProvider.KOKORO,
+            language="xx",
+            speaker_count=1,
+        )
+
+
+def test_every_speaker_is_assigned_even_when_voices_run_out():
+    """With one available voice, both speakers still get one rather than failing."""
+    catalog = get_voice_catalog()
+    voices = resolve_voices(
+        catalog=catalog, provider=TtsProvider.KOKORO, language="fr", speaker_count=2
+    )
+    assert len(voices) == 2
+
+
+def test_speaker_count_must_be_positive():
+    catalog = get_voice_catalog()
+    with pytest.raises(ValueError):
+        resolve_voices(
+            catalog=catalog, provider=TtsProvider.KOKORO, language="en", speaker_count=0
+        )