[aptos-stdlib] fix comparator tests (aptos-labs#5694)

* fix comparator tests

* fix

aptos-move/framework/aptos-stdlib/sources/comparator.move

@@ -24,6 +24,9 @@ module aptos_std::comparator {
     }
 
     // Performs a comparison of two types after BCS serialization.
+    // BCS uses little endian encoding for all integer types,
+    // so comparison between primitive integer types will not behave as expected.
+    // For example, 1(0x1) will be larger than 256(0x100) after BCS serialization.
     public fun compare<T>(left: &T, right: &T): Result {
         let left_bytes = bcs::to_bytes(left);
         let right_bytes = bcs::to_bytes(right);
@@ -81,6 +84,20 @@ module aptos_std::comparator {
         assert!(is_greater_than(&compare(&value2, &value1)), 8);
     }
 
+    #[test]
+    #[expected_failure]
+    public fun test_integer() {
+        // 1(0x1) will be larger than 256(0x100) after BCS serialization.
+        let value0: u128 = 1;
+        let value1: u128 = 256;
+
+        assert!(is_equal(&compare(&value0, &value0)), 0);
+        assert!(is_equal(&compare(&value1, &value1)), 1);
+
+        assert!(is_smaller_than(&compare(&value0, &value1)), 2);
+        assert!(is_greater_than(&compare(&value1, &value0)), 3);
+    }
+
     #[test]
     public fun test_u128() {
         let value0: u128 = 5;