🧪 Add draft version fallback helper tests

tests/ext_test.py

@@ -0,0 +1,58 @@
+"""The Sphinx extension interface module tests."""
+
+import pytest
+
+from sphinx.config import Config as SphinxConfig
+
+from sphinxcontrib.towncrier.ext import _get_draft_version_fallback
+
+
+release_sentinel = object()
+version_sentinel = object()
+
+
+@pytest.fixture
+def sphinx_config() -> SphinxConfig:
+    """Initialize a Sphinx config stub for testing."""
+    return SphinxConfig(
+        overrides={'release': release_sentinel, 'version': version_sentinel},
+    )
+
+
+@pytest.mark.parametrize(
+    ('autoversion_mode', 'expected_version'),
+    (
+        ('sphinx-release', release_sentinel),
+        ('sphinx-version', version_sentinel),
+        ('draft', '[UNRELEASED DRAFT]'),
+    ),
+)
+def test__get_draft_version_fallback_known_strategy(  # noqa: WPS116, WPS118
+        autoversion_mode: str,
+        expected_version: object,
+        sphinx_config: SphinxConfig,
+) -> None:
+    """Check that valid strategies source correct values."""
+    computed_version = _get_draft_version_fallback.__wrapped__(
+        autoversion_mode,
+        sphinx_config,
+    )
+    assert computed_version == expected_version
+
+
+@pytest.mark.parametrize('autoversion_mode', ('blah', '', 'v1.0'))
+def test__get_draft_version_fallback_invalid_strategy(  # noqa: WPS116, WPS118
+        autoversion_mode: str,
+        sphinx_config: SphinxConfig,
+) -> None:
+    """Ensure invalid strategy yields an exception."""
+    expected_error_msg = (
+        '^Expected "strategy" to be one of '
+        r"{'[\w,\s'-]+'} "
+        fr'but got {autoversion_mode !r}$'
+    )
+    with pytest.raises(ValueError, match=expected_error_msg):
+        _get_draft_version_fallback.__wrapped__(
+            autoversion_mode,
+            sphinx_config,
+        )