Add unit tests for list_ranked_articles' feed_id filtering

The sidebar's per-feed nav depends on this query correctly scoping to
one feed (or joining all of them when feed_id is None), and it's real
branching logic rather than a passthrough — exactly what the updated
Definition of Done's testing rule calls for.

Uses a throwaway SQLite file per test (migrated fresh, cleaned up via
Drop) rather than a shared fixture, since diesel-async's bb8 pool would
otherwise hand out per-connection ":memory:" databases that don't share
state.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PqTJmazHBQK878vjQ4JnnF

crates/db/src/articles.rs

@@ -152,3 +152,118 @@ impl Db {
             .collect())
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// A `Db` backed by a throwaway SQLite file under the OS temp dir,
+    /// migrated fresh per test and deleted (including its `-wal`/`-shm`
+    /// siblings) when the test finishes, so tests can't see each other's
+    /// data or leak files across runs.
+    struct TestDb {
+        db: Db,
+        path: std::path::PathBuf,
+    }
+
+    impl std::ops::Deref for TestDb {
+        type Target = Db;
+        fn deref(&self) -> &Db {
+            &self.db
+        }
+    }
+
+    impl Drop for TestDb {
+        fn drop(&mut self) {
+            for suffix in ["", "-wal", "-shm"] {
+                let _ = std::fs::remove_file(format!("{}{suffix}", self.path.display()));
+            }
+        }
+    }
+
+    async fn test_db() -> TestDb {
+        let path = std::env::temp_dir().join(format!("feedsignal-test-{}.db", Uuid::new_v4()));
+        let db = Db::connect(path.to_str().unwrap())
+            .await
+            .expect("connect test db");
+        TestDb { db, path }
+    }
+
+    fn article(feed_id: Uuid, final_score: f32) -> Article {
+        Article {
+            id: Uuid::new_v4(),
+            feed_id,
+            url: format!("https://example.com/{}", Uuid::new_v4()),
+            title: "Title".to_string(),
+            summary: "Summary".to_string(),
+            published_at: None,
+            topics: vec![],
+            embedding_score: None,
+            llm_score: None,
+            final_score: Some(final_score),
+            estimated_read_seconds: None,
+        }
+    }
+
+    /// `feed_id: None` joins every subscribed feed's articles into one
+    /// ranked list — what the sidebar's "All" view depends on.
+    #[tokio::test]
+    async fn list_ranked_articles_with_no_feed_filter_returns_every_feed() {
+        let db = test_db().await;
+        let feed_a = db
+            .upsert_feed("https://a.example.com/feed", "Feed A")
+            .await
+            .unwrap();
+        let feed_b = db
+            .upsert_feed("https://b.example.com/feed", "Feed B")
+            .await
+            .unwrap();
+        db.insert_article(&article(feed_a, 0.9)).await.unwrap();
+        db.insert_article(&article(feed_b, 0.5)).await.unwrap();
+
+        let rows = db.list_ranked_articles(None, 10).await.unwrap();
+
+        assert_eq!(rows.len(), 2);
+    }
+
+    /// `feed_id: Some(id)` scopes the list to that one feed and excludes
+    /// every other subscribed feed's articles — what the sidebar's
+    /// per-feed nav depends on.
+    #[tokio::test]
+    async fn list_ranked_articles_with_feed_filter_excludes_other_feeds() {
+        let db = test_db().await;
+        let feed_a = db
+            .upsert_feed("https://a.example.com/feed", "Feed A")
+            .await
+            .unwrap();
+        let feed_b = db
+            .upsert_feed("https://b.example.com/feed", "Feed B")
+            .await
+            .unwrap();
+        db.insert_article(&article(feed_a, 0.9)).await.unwrap();
+        db.insert_article(&article(feed_b, 0.5)).await.unwrap();
+
+        let rows = db.list_ranked_articles(Some(feed_a), 10).await.unwrap();
+
+        assert_eq!(rows.len(), 1);
+        assert_eq!(rows[0].1, feed_a.to_string());
+    }
+
+    /// Results stay ordered by `final_score` descending regardless of
+    /// insertion order, matching how the UI ranks the article list.
+    #[tokio::test]
+    async fn list_ranked_articles_orders_by_final_score_descending() {
+        let db = test_db().await;
+        let feed = db
+            .upsert_feed("https://a.example.com/feed", "Feed A")
+            .await
+            .unwrap();
+        db.insert_article(&article(feed, 0.2)).await.unwrap();
+        db.insert_article(&article(feed, 0.8)).await.unwrap();
+
+        let rows = db.list_ranked_articles(None, 10).await.unwrap();
+
+        assert_eq!(rows[0].6, Some(0.8));
+        assert_eq!(rows[1].6, Some(0.2));
+    }
+}