src/scene.rs

@@ -259,4 +259,25 @@ mod tests {
         assert_eq!(s.camera, Camera::default());
         assert_eq!(s.light, Light::default());
     }
-}
+
+    #[test]
+    fn hydrology_default_generates_distinct_lake_and_river_shapes() {
+        let h = Hydrology::default();
+        assert!(h.lake_radius > 0.0);
+        assert!(h.river_width > 0.0);
+        assert!(h.lake_coverage(h.lake_center_x, h.lake_center_z) > 0.9);
+        assert!(h.river_coverage(h.river_center_x, 0.5) > 0.5);
+        assert!(h.lake_coverage(0.0, 0.0) < 0.2);
+    }
+
+    #[test]
+    fn hydrology_clamps_and_falls_off_with_distance() {
+        let h = Hydrology {
+            river_bend: 0.0,
+            ..Hydrology::default()
+        };
+        let center = h.lake_coverage(h.lake_center_x, h.lake_center_z);
+        let far = h.lake_coverage(0.95, 0.05);
+        assert!(center > far);
+        assert!(h.river_coverage(h.river_center_x, 0.5) > h.river_coverage(0.0, 0.5));
+    }