test: cover the find_immutables_dir function to show recursivity

Author: turmelclem

internal/cardano-node/mithril-cardano-node-internal-database/src/entities/immutable_file.rs

@@ -426,6 +426,33 @@ mod tests {
         );
     }
 
+    #[test]
+    fn find_immutables_dir_returns_none_if_no_immutable_dir_found() {
+        let database_path = temp_dir_create!();
+        assert!(find_immutables_dir(&database_path).is_none());
+    }
+
+    #[test]
+    fn find_immutables_dir_returns_immutable_dir_if_found_at_root() {
+        let database_path = temp_dir_create!();
+        fs::create_dir(database_path.join(IMMUTABLE_DIR)).unwrap();
+
+        let immutable_dir =
+            find_immutables_dir(&database_path).expect("Immutable directory should be found");
+        assert_eq!(immutable_dir, database_path.join(IMMUTABLE_DIR));
+    }
+
+    #[test]
+    fn find_immutables_dir_returns_immutable_dir_if_found_at_any_depth() {
+        let database_path = temp_dir_create!();
+        let subdir = database_path.join("one/two/three");
+        fs::create_dir_all(subdir.join(IMMUTABLE_DIR)).unwrap();
+
+        let immutable_dir =
+            find_immutables_dir(&database_path).expect("Immutable directory should be found");
+        assert_eq!(immutable_dir, subdir.join(IMMUTABLE_DIR));
+    }
+
     #[test]
     fn at_least_one_immutable_files_exist_in_dir_throw_error_if_immutable_dir_is_empty() {
         let database_path = temp_dir_create!();