fix: publish feeds atomically

tests/test_postprocessing.py

@@ -0,0 +1,52 @@
+from pathlib import Path
+
+import pytest
+
+from repub.config import feed_output_path, staged_feed_output_path
+from repub.postprocessing import publish_staged_feed
+
+VALID_FEED = '<rss version="2.0"><channel><title>new</title></channel></rss>\n'
+
+
+def test_publish_staged_feed_replaces_public_feed(tmp_path: Path) -> None:
+    out_dir = tmp_path / "out"
+    public_path = feed_output_path(out_dir=out_dir, feed_slug="demo")
+    staged_path = staged_feed_output_path(out_dir=out_dir, feed_slug="demo")
+    public_path.parent.mkdir(parents=True)
+    public_path.write_text("<rss>old</rss>\n", encoding="utf-8")
+    staged_path.write_text(VALID_FEED, encoding="utf-8")
+
+    published_path = publish_staged_feed(out_dir=out_dir, feed_slug="demo")
+
+    assert published_path == public_path
+    assert public_path.read_text(encoding="utf-8") == VALID_FEED
+    assert not staged_path.exists()
+
+
+def test_publish_staged_feed_requires_staged_file(tmp_path: Path) -> None:
+    with pytest.raises(FileNotFoundError):
+        publish_staged_feed(out_dir=tmp_path / "out", feed_slug="missing")
+
+
+@pytest.mark.parametrize(
+    "staged_feed",
+    [
+        '<rss version="2.0"/>\n',
+        '<rss version="2.0"><channel></rss>\n',
+    ],
+)
+def test_publish_staged_feed_rejects_unusable_feed(
+    tmp_path: Path, staged_feed: str
+) -> None:
+    out_dir = tmp_path / "out"
+    public_path = feed_output_path(out_dir=out_dir, feed_slug="demo")
+    staged_path = staged_feed_output_path(out_dir=out_dir, feed_slug="demo")
+    public_path.parent.mkdir(parents=True)
+    public_path.write_text("<rss>old</rss>\n", encoding="utf-8")
+    staged_path.write_text(staged_feed, encoding="utf-8")
+
+    with pytest.raises(ValueError):
+        publish_staged_feed(out_dir=out_dir, feed_slug="demo")
+
+    assert public_path.read_text(encoding="utf-8") == "<rss>old</rss>\n"
+    assert staged_path.read_text(encoding="utf-8") == staged_feed