feat: store supported voices in TTSBackendMetadata

Add voices field to TTSBackendMetadata so each backend's supported
voice list is part of its metadata rather than external constants.

- Add voices: tuple[str, ...] = () to TTSBackendMetadata
- Create _KOKORO_METADATA / _SUPERTONIC_METADATA as single source
  of truth for both metadata property and registry registration
- Update KokoroBackend.get_available_voices() to use self.metadata.voices
- Update SupertonicBackend.get_available_voices() to use self.metadata.voices
- Add tests for voices field, metadata voice content, and unified instance identity

abogen/tts_backend.py

@@ -18,11 +18,13 @@ class TTSBackendMetadata:
         id: Unique backend identifier (e.g. ``"kokoro"``, ``"supertonic"``).
         name: Human-readable display name.
         description: Short description of the backend.
+        voices: Tuple of supported voice identifiers.
     """
 
     id: str
     name: str
     description: str
+    voices: tuple[str, ...] = ()
 
 
 class TTSBackend(Protocol):

abogen/tts_backends/kokoro.py

@@ -10,6 +10,16 @@ from typing import Any, Dict, Iterator, List, Optional
 
 import numpy as np
 
+from abogen.constants import VOICES_INTERNAL
+from abogen.tts_backend import TTSBackendMetadata
+
+_KOKORO_METADATA = TTSBackendMetadata(
+    id="kokoro",
+    name="Kokoro",
+    description="Kokoro TTS engine",
+    voices=tuple(VOICES_INTERNAL),
+)
+
 
 def _load_kpipeline():
     """Lazy-load Kokoro dependencies."""
@@ -39,14 +49,8 @@ class KokoroBackend:
         self._lang_code = lang_code
 
     @property
-    def metadata(self):
+    def metadata(self) -> TTSBackendMetadata:
-        from abogen.tts_backend import TTSBackendMetadata
+        return _KOKORO_METADATA
-
-        return TTSBackendMetadata(
-            id="kokoro",
-            name="Kokoro",
-            description="Kokoro TTS engine",
-        )
 
     def __call__(
         self,
@@ -89,9 +93,7 @@ class KokoroBackend:
 
     def get_available_voices(self) -> List[str]:
         """Return known Kokoro voice identifiers."""
-        from abogen.constants import VOICES_INTERNAL
+        return list(self.metadata.voices)
-
-        return list(VOICES_INTERNAL)
 
     def get_supported_formats(self) -> List[str]:
         """Kokoro outputs raw PCM float32 audio."""
@@ -111,14 +113,9 @@ def create_kokoro_backend(**kwargs: Any) -> KokoroBackend:
 
 
 # --- Registration ---
-from abogen.tts_backend import TTSBackendMetadata  # noqa: E402
 from abogen.tts_backend_registry import register_backend  # noqa: E402
 
 register_backend(
-    metadata=TTSBackendMetadata(
+    metadata=_KOKORO_METADATA,
-        id="kokoro",
-        name="Kokoro",
-        description="Kokoro TTS engine",
-    ),
     factory=create_kokoro_backend,
 )

abogen/tts_backends/supertonic.py

@@ -15,6 +15,15 @@ logger = logging.getLogger(__name__)
 
 DEFAULT_SUPERTONIC_VOICES = ("M1", "M2", "M3", "M4", "M5", "F1", "F2", "F3", "F4", "F5")
 
+from abogen.tts_backend import TTSBackendMetadata
+
+_SUPERTONIC_METADATA = TTSBackendMetadata(
+    id="supertonic",
+    name="SuperTonic",
+    description="SuperTonic TTS engine",
+    voices=DEFAULT_SUPERTONIC_VOICES,
+)
+
 
 @dataclass
 class SupertonicSegment:
@@ -282,12 +291,8 @@ class SupertonicBackend:
     """
 
     @property
-    def metadata(self) -> "TTSBackendMetadata":
+    def metadata(self) -> TTSBackendMetadata:
-        return TTSBackendMetadata(
+        return _SUPERTONIC_METADATA
-            id="supertonic",
-            name="SuperTonic",
-            description="SuperTonic TTS engine",
-        )
 
     def __init__(self, **kwargs: Any) -> None:
         self._pipeline = SupertonicPipeline(
@@ -333,7 +338,7 @@ class SupertonicBackend:
 
     def get_available_voices(self) -> List[str]:
         """Return the list of built-in SuperTonic voice identifiers."""
-        return list(DEFAULT_SUPERTONIC_VOICES)
+        return list(self.metadata.voices)
 
     def get_supported_formats(self) -> List[str]:
         return ["wav"]
@@ -379,14 +384,9 @@ def create_supertonic_backend(**kwargs: Any) -> SupertonicBackend:
     return SupertonicBackend(**kwargs)
 
 
-from abogen.tts_backend import TTSBackendMetadata
+from abogen.tts_backend_registry import register_backend  # noqa: E402
-from abogen.tts_backend_registry import register_backend
 
 register_backend(
-    metadata=TTSBackendMetadata(
+    metadata=_SUPERTONIC_METADATA,
-        id="supertonic",
-        name="SuperTonic",
-        description="SuperTonic TTS engine",
-    ),
     factory=create_supertonic_backend,
 )

tests/test_tts_backend.py

@@ -1,149 +1,204 @@
-from dataclasses import dataclass
+from dataclasses import dataclass
-
+
-from abogen.tts_backend import TTSBackendMetadata
+from abogen.tts_backend import TTSBackendMetadata
-from abogen.tts_backend_registry import TTSBackendRegistry
+from abogen.tts_backend_registry import TTSBackendRegistry
-
+
-
+
-class TestTTSBackendMetadata:
+class TestTTSBackendMetadata:
-    def test_is_frozen_dataclass(self):
+    def test_is_frozen_dataclass(self):
-        assert dataclass(TTSBackendMetadata)
+        assert dataclass(TTSBackendMetadata)
-
+
-    def test_fields_are_present(self):
+    def test_fields_are_present(self):
-        meta = TTSBackendMetadata(
+        meta = TTSBackendMetadata(
-            id="test",
+            id="test",
-            name="Test Backend",
+            name="Test Backend",
-            description="A test backend",
+            description="A test backend",
-        )
+        )
-        assert meta.id == "test"
+        assert meta.id == "test"
-        assert meta.name == "Test Backend"
+        assert meta.name == "Test Backend"
-        assert meta.description == "A test backend"
+        assert meta.description == "A test backend"
-
+
-    def test_is_immutable(self):
+    def test_voices_field_default_empty(self):
-        import pytest
+        meta = TTSBackendMetadata(
-
+            id="test",
-        meta = TTSBackendMetadata(
+            name="Test",
-            id="kokoro",
+            description="Test backend",
-            name="Kokoro",
+        )
-            description="Test",
+        assert meta.voices == ()
-        )
+
-        with pytest.raises(Exception):
+    def test_voices_field_stored(self):
-            meta.id = "changed"
+        meta = TTSBackendMetadata(
-
+            id="test",
-
+            name="Test",
-class TestTTSBackendRegistry:
+            description="Test backend",
-    def test_register_and_list(self):
+            voices=("v1", "v2"),
-        registry = TTSBackendRegistry()
+        )
-        meta = TTSBackendMetadata(id="a", name="A", description="Backend A")
+        assert meta.voices == ("v1", "v2")
-        registry.register(metadata=meta, factory=lambda: None)
+
-
+    def test_is_immutable(self):
-        backends = registry.list_backends()
+        import pytest
-        assert len(backends) == 1
+
-        assert backends[0].id == "a"
+        meta = TTSBackendMetadata(
-
+            id="kokoro",
-    def test_list_multiple(self):
+            name="Kokoro",
-        registry = TTSBackendRegistry()
+            description="Test",
-        meta_a = TTSBackendMetadata(id="a", name="A", description="A")
+        )
-        meta_b = TTSBackendMetadata(id="b", name="B", description="B")
+        with pytest.raises(Exception):
-        registry.register(metadata=meta_a, factory=lambda: None)
+            meta.id = "changed"
-        registry.register(metadata=meta_b, factory=lambda: None)
+
-
+
-        backends = registry.list_backends()
+class TestTTSBackendRegistry:
-        ids = [b.id for b in backends]
+    def test_register_and_list(self):
-        assert "a" in ids
+        registry = TTSBackendRegistry()
-        assert "b" in ids
+        meta = TTSBackendMetadata(id="a", name="A", description="Backend A")
-
+        registry.register(metadata=meta, factory=lambda: None)
-    def test_get_metadata(self):
+
-        registry = TTSBackendRegistry()
+        backends = registry.list_backends()
-        meta = TTSBackendMetadata(id="x", name="X", description="X backend")
+        assert len(backends) == 1
-        registry.register(metadata=meta, factory=lambda: None)
+        assert backends[0].id == "a"
-
+
-        result = registry.get_metadata("x")
+    def test_list_multiple(self):
-        assert result.id == "x"
+        registry = TTSBackendRegistry()
-        assert result.name == "X"
+        meta_a = TTSBackendMetadata(id="a", name="A", description="A")
-
+        meta_b = TTSBackendMetadata(id="b", name="B", description="B")
-    def test_get_metadata_unknown_raises(self):
+        registry.register(metadata=meta_a, factory=lambda: None)
-        import pytest
+        registry.register(metadata=meta_b, factory=lambda: None)
-
+
-        registry = TTSBackendRegistry()
+        backends = registry.list_backends()
-        with pytest.raises(KeyError, match="Unknown backend: nope"):
+        ids = [b.id for b in backends]
-            registry.get_metadata("nope")
+        assert "a" in ids
-
+        assert "b" in ids
-    def test_create_backend(self):
+
-        registry = TTSBackendRegistry()
+    def test_get_metadata(self):
-        meta = TTSBackendMetadata(id="test", name="Test", description="Test backend")
+        registry = TTSBackendRegistry()
-
+        meta = TTSBackendMetadata(id="x", name="X", description="X backend")
-        def factory(**kwargs):
+        registry.register(metadata=meta, factory=lambda: None)
-            return {"created": True, "kwargs": kwargs}
+
-
+        result = registry.get_metadata("x")
-        registry.register(metadata=meta, factory=factory)
+        assert result.id == "x"
-        result = registry.create_backend("test", foo="bar")
+        assert result.name == "X"
-
+
-        assert result == {"created": True, "kwargs": {"foo": "bar"}}
+    def test_get_metadata_unknown_raises(self):
-
+        import pytest
-    def test_create_backend_unknown_raises(self):
+
-        import pytest
+        registry = TTSBackendRegistry()
-
+        with pytest.raises(KeyError, match="Unknown backend: nope"):
-        registry = TTSBackendRegistry()
+            registry.get_metadata("nope")
-        with pytest.raises(KeyError, match="Unknown backend: missing"):
+
-            registry.create_backend("missing")
+    def test_create_backend(self):
-
+        registry = TTSBackendRegistry()
-    def test_register_overwrites(self):
+        meta = TTSBackendMetadata(id="test", name="Test", description="Test backend")
-        registry = TTSBackendRegistry()
+
-        meta1 = TTSBackendMetadata(id="x", name="V1", description="First")
+        def factory(**kwargs):
-        meta2 = TTSBackendMetadata(id="x", name="V2", description="Second")
+            return {"created": True, "kwargs": kwargs}
-        registry.register(metadata=meta1, factory=lambda: "v1")
+
-        registry.register(metadata=meta2, factory=lambda: "v2")
+        registry.register(metadata=meta, factory=factory)
-
+        result = registry.create_backend("test", foo="bar")
-        result = registry.get_metadata("x")
+
-        assert result.name == "V2"
+        assert result == {"created": True, "kwargs": {"foo": "bar"}}
-        assert registry.create_backend("x") == "v2"
+
-
+    def test_create_backend_unknown_raises(self):
-
+        import pytest
-class TestBackendRegistration:
+
-    """Tests that existing backends are auto-registered."""
+        registry = TTSBackendRegistry()
-
+        with pytest.raises(KeyError, match="Unknown backend: missing"):
-    def test_import_triggers_registration(self):
+            registry.create_backend("missing")
-        import abogen.tts_backends  # noqa: F401
+
-
+    def test_register_overwrites(self):
-        from abogen.tts_backend_registry import _registry
+        registry = TTSBackendRegistry()
-
+        meta1 = TTSBackendMetadata(id="x", name="V1", description="First")
-        backends = _registry.list_backends()
+        meta2 = TTSBackendMetadata(id="x", name="V2", description="Second")
-        ids = [b.id for b in backends]
+        registry.register(metadata=meta1, factory=lambda: "v1")
-        assert "kokoro" in ids
+        registry.register(metadata=meta2, factory=lambda: "v2")
-        assert "supertonic" in ids
+
-
+        result = registry.get_metadata("x")
-    def test_kokoro_metadata(self):
+        assert result.name == "V2"
-        import abogen.tts_backends  # noqa: F401
+        assert registry.create_backend("x") == "v2"
-
+
-        from abogen.tts_backend_registry import _registry
+
-
+class TestBackendRegistration:
-        meta = _registry.get_metadata("kokoro")
+    """Tests that existing backends are auto-registered."""
-        assert meta.id == "kokoro"
+
-        assert meta.name == "Kokoro"
+    def test_import_triggers_registration(self):
-        assert "Kokoro" in meta.description
+        import abogen.tts_backends  # noqa: F401
-
+
-    def test_supertonic_metadata(self):
+        from abogen.tts_backend_registry import _registry
-        import abogen.tts_backends  # noqa: F401
+
-
+        backends = _registry.list_backends()
-        from abogen.tts_backend_registry import _registry
+        ids = [b.id for b in backends]
-
+        assert "kokoro" in ids
-        meta = _registry.get_metadata("supertonic")
+        assert "supertonic" in ids
-        assert meta.id == "supertonic"
+
-        assert meta.name == "SuperTonic"
+    def test_kokoro_metadata(self):
-        assert "SuperTonic" in meta.description
+        import abogen.tts_backends  # noqa: F401
-
+
-    def test_kokoro_factory_callable(self):
+        from abogen.tts_backend_registry import _registry
-        import abogen.tts_backends  # noqa: F401
+
-
+        meta = _registry.get_metadata("kokoro")
-        from abogen.tts_backend_registry import _registry
+        assert meta.id == "kokoro"
-
+        assert meta.name == "Kokoro"
-        factory = _registry._factories["kokoro"]
+        assert "Kokoro" in meta.description
-        assert callable(factory)
+
-
+    def test_supertonic_metadata(self):
-    def test_supertonic_factory_callable(self):
+        import abogen.tts_backends  # noqa: F401
-        import abogen.tts_backends  # noqa: F401
+
-
+        from abogen.tts_backend_registry import _registry
-        from abogen.tts_backend_registry import _registry
+
-
+        meta = _registry.get_metadata("supertonic")
-        factory = _registry._factories["supertonic"]
+        assert meta.id == "supertonic"
-        assert callable(factory)
+        assert meta.name == "SuperTonic"
+        assert "SuperTonic" in meta.description
+
+    def test_kokoro_metadata_has_voices(self):
+        import abogen.tts_backends  # noqa: F401
+
+        from abogen.tts_backend_registry import _registry
+
+        meta = _registry.get_metadata("kokoro")
+        assert isinstance(meta.voices, tuple)
+        assert len(meta.voices) > 0
+        assert all(isinstance(v, str) for v in meta.voices)
+
+    def test_supertonic_metadata_has_voices(self):
+        import abogen.tts_backends  # noqa: F401
+
+        from abogen.tts_backend_registry import _registry
+
+        meta = _registry.get_metadata("supertonic")
+        assert isinstance(meta.voices, tuple)
+        assert len(meta.voices) == 10
+        assert meta.voices == ("M1", "M2", "M3", "M4", "M5", "F1", "F2", "F3", "F4", "F5")
+
+    def test_kokoro_factory_callable(self):
+        import abogen.tts_backends  # noqa: F401
+
+        from abogen.tts_backend_registry import _registry
+
+        factory = _registry._factories["kokoro"]
+        assert callable(factory)
+
+    def test_supertonic_factory_callable(self):
+        import abogen.tts_backends  # noqa: F401
+
+        from abogen.tts_backend_registry import _registry
+
+        factory = _registry._factories["supertonic"]
+        assert callable(factory)
+
+    def test_kokoro_metadata_voices_match_registry(self):
+        """Ensure the metadata property on the instance shares voices with registry."""
+        from abogen.tts_backends.kokoro import _KOKORO_METADATA
+        from abogen.tts_backend_registry import _registry
+
+        registry_meta = _registry.get_metadata("kokoro")
+        assert _KOKORO_METADATA is registry_meta
+        assert _KOKORO_METADATA.voices == registry_meta.voices
+
+    def test_supertonic_metadata_voices_match_registry(self):
+        """Ensure the metadata property on the instance shares voices with registry."""
+        from abogen.tts_backends.supertonic import _SUPERTONIC_METADATA
+        from abogen.tts_backend_registry import _registry
+
+        registry_meta = _registry.get_metadata("supertonic")
+        assert _SUPERTONIC_METADATA is registry_meta
+        assert _SUPERTONIC_METADATA.voices == registry_meta.voices