fix: add check to prevent naive implementation of is_international

* fix(structs3): Add check to prevent naive implementation

* chore(structs3): Add a missed newline after the test I added

exercises/structs/structs3.rs

@@ -57,6 +57,16 @@ mod tests {
         assert!(package.is_international());
     }
 
+    #[test]
+    fn create_local_package() {
+        let sender_country = String::from("Canada");
+        let recipient_country = sender_country.clone();
+
+        let package = Package::new(sender_country, recipient_country, 1200);
+
+        assert!(!package.is_international());
+    }
+
     #[test]
     fn calculate_transport_fees() {
         let sender_country = String::from("Spain");