Additional tests for using for directive

test/libsolidity/semanticTests/using/attach_function_as_a_member_and_as_an_operator.sol

@@ -0,0 +1,21 @@
+type Int is int16;
+
+using {add as +, add} for Int;
+
+function add(Int _a, Int _b) pure returns (Int) {
+    return Int.wrap(Int.unwrap(_a) + Int.unwrap(_b));
+}
+
+contract C {
+    function f() pure public returns (Int) {
+        return Int.wrap(5) + Int.wrap(5);
+    }
+
+    function g() pure public returns (Int) {
+        return Int.wrap(7).add(Int.wrap(6));
+    }
+}
+
+// ----
+// f() -> 10
+// g() -> 13