Add additional initial value tests

test/intl402/NumberFormat/prototype/toStringTag/initial-value.js

@@ -12,3 +12,13 @@ assert.sameValue(
   Object.prototype.toString.call(new Intl.NumberFormat()),
   '[object Object]'
 );
+
+Object.defineProperty(Intl.NumberFormat.prototype, Symbol.toStringTag, {
+  value: 'Alpha'
+});
+
+assert.sameValue(Intl.NumberFormat.prototype[Symbol.toStringTag], 'Alpha');
+assert.sameValue(
+  Object.prototype.toString.call(new Intl.NumberFormat()),
+  '[object Alpha]'
+);

test/intl402/NumberFormat/prototype/toStringTag/prop-desc.js

@@ -8,7 +8,7 @@ description: >
 includes: [propertyHelper.js]
 ---*/
 
-verifyProperty(Intl.NumberFormat, Symbol.toStringTag, {
+verifyProperty(Intl.NumberFormat.prototype, Symbol.toStringTag, {
   writable: false,
   enumerable: false,
   configurable: true