fix(speech): define the Kokoro optional install contract (#5962)

tests/test_kokoro_optional_requirements.py

@@ -0,0 +1,40 @@
+from pathlib import Path
+
+import pytest
+from packaging.requirements import Requirement
+
+
+ROOT = Path(__file__).resolve().parents[1]
+
+
+def _optional_requirement(name):
+    lines = (ROOT / "requirements-optional.txt").read_text(encoding="utf-8").splitlines()
+    return Requirement(next(line for line in lines if line.startswith(name)))
+
+
+def test_kokoro_optional_dependency_pins_the_verified_release():
+    kokoro = _optional_requirement("kokoro")
+
+    assert str(kokoro.specifier) == "==0.9.4"
+
+
+@pytest.mark.parametrize(
+    ("python_version", "selected"),
+    (("3.11", True), ("3.12", True), ("3.13", False), ("3.14", False)),
+)
+def test_kokoro_feature_markers_match_supported_python_range(python_version, selected):
+    for name in ("kokoro", "soundfile"):
+        requirement = _optional_requirement(name)
+        assert requirement.marker is not None
+        assert requirement.marker.evaluate({"python_version": python_version}) is selected
+
+
+def test_setup_documents_container_constraint_and_install_command():
+    setup = (ROOT / "docs" / "setup.md").read_text(encoding="utf-8")
+
+    assert "pip install -r requirements-optional.txt" in setup
+    assert "default Docker image currently uses Python 3.14" in setup
+    assert "Python `>=3.10,<3.13`" in setup
+    assert "native Python 3.11 or 3.12" in setup
+    assert "skipped on Python 3.13+" in setup
+    assert "torch build has CUDA" in setup