Add node ring testing

src/hasher.rs

@@ -112,4 +112,67 @@ mod tests {
             );
         }
     }
+
+    #[test]
+    fn test_ring_stability_on_add() {
+        // Adding a 4th volume to a 3-volume ring should only move ~25% of keys
+        let volumes: Vec<String> = (1..=3).map(|i| format!("http://vol{i}")).collect();
+        let ring_before = Ring::new(&volumes, 100);
+
+        let mut volumes4 = volumes.clone();
+        volumes4.push("http://vol4".into());
+        let ring_after = Ring::new(&volumes4, 100);
+
+        let total = 10000;
+        let mut moved = 0;
+        for i in 0..total {
+            let key = format!("key-{i}");
+            let before = &ring_before.get_volumes(&key, 1)[0];
+            let after = &ring_after.get_volumes(&key, 1)[0];
+            if before != after {
+                moved += 1;
+            }
+        }
+
+        // Ideal: 1/4 of keys move (25%). Allow 15%-40%.
+        let pct = moved as f64 / total as f64 * 100.0;
+        assert!(
+            pct > 15.0 && pct < 40.0,
+            "expected ~25% of keys to move, got {pct:.1}% ({moved}/{total})"
+        );
+    }
+
+    #[test]
+    fn test_ring_stability_on_remove() {
+        // Removing 1 volume from a 4-volume ring should only move ~25% of keys
+        let volumes: Vec<String> = (1..=4).map(|i| format!("http://vol{i}")).collect();
+        let ring_before = Ring::new(&volumes, 100);
+
+        let volumes3: Vec<String> = (1..=3).map(|i| format!("http://vol{i}")).collect();
+        let ring_after = Ring::new(&volumes3, 100);
+
+        let total = 10000;
+        let mut moved = 0;
+        for i in 0..total {
+            let key = format!("key-{i}");
+            let before = &ring_before.get_volumes(&key, 1)[0];
+            let after = &ring_after.get_volumes(&key, 1)[0];
+            if before != after {
+                moved += 1;
+            }
+        }
+
+        // Ideal: 1/4 of keys move (25%). Allow 15%-40%.
+        let pct = moved as f64 / total as f64 * 100.0;
+        assert!(
+            pct > 15.0 && pct < 40.0,
+            "expected ~25% of keys to move, got {pct:.1}% ({moved}/{total})"
+        );
+    }
+
+    #[test]
+    fn test_ring_empty() {
+        let ring = Ring::new(&[], 100);
+        assert_eq!(ring.get_volumes("key", 1), Vec::<String>::new());
+    }
 }