diff --git a/01.workspace/heave/src/imp/catalog_delete.rs b/01.workspace/heave/src/imp/catalog_delete.rs
index 539a947..31e1264 100644
--- a/01.workspace/heave/src/imp/catalog_delete.rs
+++ b/01.workspace/heave/src/imp/catalog_delete.rs
@@ -16,7 +16,7 @@ impl Catalog {
     /// # Arguments
     ///
     /// * `id` - The ID of the entity to mark for deletion.
-    pub fn delete(&mut self, id: &str) {
+    pub fn delete(&self, id: &str) {
         let _ = self.on_items(|items| {
             let entity = items.get_mut(id);
             if let Some(entity) = entity {
diff --git a/01.workspace/heave/src/tst/catalog_delete.rs b/01.workspace/heave/src/tst/catalog_delete.rs
index 5376998..7afb7b1 100644
--- a/01.workspace/heave/src/tst/catalog_delete.rs
+++ b/01.workspace/heave/src/tst/catalog_delete.rs
@@ -4,7 +4,7 @@ mod tests {
     #[test]
     fn delete_should_mark_entity_as_to_delete() {
         // Should mark an existing entity's state as 'ToDelete'.
-        let mut catalog = Catalog::new("dummy.db");
+        let catalog = Catalog::new("dummy.db");
         let item = Item {
             id: "item-123".to_string(),
             name: "Test Item".to_string(),
@@ -27,7 +27,7 @@ mod tests {
     #[test]
     fn delete_should_have_no_effect_for_nonexistent_id() {
         // Should have no effect if the entity ID does not exist.
-        let mut catalog = Catalog::new("dummy.db");
+        let catalog = Catalog::new("dummy.db");
         let item = Item {
             id: "item-123".to_string(),
             name: "Test Item".to_string(),
diff --git a/01.workspace/heave/src/tst/catalog_persist.rs b/01.workspace/heave/src/tst/catalog_persist.rs
index faf5708..fb3be35 100644
--- a/01.workspace/heave/src/tst/catalog_persist.rs
+++ b/01.workspace/heave/src/tst/catalog_persist.rs
@@ -43,7 +43,7 @@ mod tests {
             std::fs::remove_file(path).unwrap();
         }
         // 1. Create catalog, insert an item, and persist it.
-        let mut catalog1 = Catalog::new(db_path);
+        let catalog1 = Catalog::new(db_path);
         catalog1.init().unwrap();
         let item1 = Item {
             id: "item-to-delete".to_string(),
@@ -248,7 +248,7 @@ mod tests {
             std::fs::remove_file(path).unwrap();
         }
         // 1. Setup: Create a catalog and pre-populate it with some data.
-        let mut catalog = Catalog::new(db_path);
+        let catalog = Catalog::new(db_path);
         catalog.init().unwrap();
         let item_to_update = Item {
             id: "update-me".to_string(),