feat: Add test to increase coverage of naive permutations (#687)

* feat: add test to cover empty array in naive

* tests: check `permute` against empty input

---------

Co-authored-by: Piotr Idzik <[email protected]>

Author: realstealthninja

src/general/permutations/naive.rs

@@ -96,6 +96,13 @@ mod tests {
         }
     }
 
+    #[test]
+    fn empty_array() {
+        let empty: std::vec::Vec<u8> = vec![];
+        assert_eq!(permute(&empty), vec![vec![]]);
+        assert_eq!(permute_unique(&empty), vec![vec![]]);
+    }
+
     #[test]
     fn test_3_times_the_same_value() {
         let original = vec![1, 1, 1];