Merge branch 'james/mainline/checked-amounts' (#748) into main

Checked arithmetic was also brought in by other branches, but this one
is the only one with the tests.

* james/mainline/checked-amounts:
  [ci] wasm checksums update
  Add changelog
  Add tests for Amount checked arithmetic
  Add Amount::checked_add method

.changelog/unreleased/improvements/748-checked-amounts.md

@@ -0,0 +1,2 @@
+- Complete checked arithmetic for Amount type
+  ([#748](https://github.com/anoma/namada/issues/748))

core/src/types/token.rs

@@ -519,6 +519,37 @@ mod tests {
         let zero = Amount::from(0);
         assert_eq!("0", zero.to_string());
     }
+
+    #[test]
+    fn test_amount_checked_sub() {
+        let max = Amount::from(u64::MAX);
+        let one = Amount::from(1);
+        let zero = Amount::from(0);
+
+        assert_eq!(zero.checked_sub(zero), Some(zero));
+        assert_eq!(zero.checked_sub(one), None);
+        assert_eq!(zero.checked_sub(max), None);
+
+        assert_eq!(max.checked_sub(zero), Some(max));
+        assert_eq!(max.checked_sub(one), Some(max - one));
+        assert_eq!(max.checked_sub(max), Some(zero));
+    }
+
+    #[test]
+    fn test_amount_checked_add() {
+        let max = Amount::from(u64::MAX);
+        let one = Amount::from(1);
+        let zero = Amount::from(0);
+
+        assert_eq!(zero.checked_add(zero), Some(zero));
+        assert_eq!(zero.checked_add(one), Some(one));
+        assert_eq!(zero.checked_add(max - one), Some(max - one));
+        assert_eq!(zero.checked_add(max), Some(max));
+
+        assert_eq!(max.checked_add(zero), Some(max));
+        assert_eq!(max.checked_add(one), None);
+        assert_eq!(max.checked_add(max), None);
+    }
 }
 
 /// Helpers for testing with addresses.