Object.prototype.toString: avoid over-DRYness, and add preconditions

test/built-ins/Object/prototype/toString/symbol-tag-non-str-builtin.js

@@ -15,62 +15,65 @@ features: [Symbol.toStringTag, Symbol.iterator, generators, WeakMap]
 ---*/
 
 var toString = Object.prototype.toString;
-var defaultTag = '[object Object]';
 
 delete Symbol.prototype[Symbol.toStringTag];
-assert.sameValue(toString.call(Symbol('desc')), defaultTag);
+assert.sameValue(toString.call(Symbol('desc')), '[object Object]');
 
 Object.defineProperty(Math, Symbol.toStringTag, {value: Symbol()});
-assert.sameValue(toString.call(Math), defaultTag);
+assert.sameValue(toString.call(Math), '[object Object]');
 
 var strIter = ''[Symbol.iterator]();
 var strIterProto = Object.getPrototypeOf(strIter);
+assert.sameValue(toString.call(strIter), '[object String Iterator]');
 delete strIterProto[Symbol.toStringTag];
-assert.sameValue(toString.call(strIter), defaultTag);
+assert.sameValue(toString.call(strIter), '[object Object]');
 
 var arrIter = [][Symbol.iterator]();
 var arrIterProto = Object.getPrototypeOf(arrIter)
+assert.sameValue(toString.call(arrIter), '[object Array Iterator]');
 Object.defineProperty(arrIterProto, Symbol.toStringTag, {value: null});
-assert.sameValue(toString.call(arrIter), defaultTag);
+assert.sameValue(toString.call(arrIter), '[object Object]');
 
 var map = new Map();
 delete Map.prototype[Symbol.toStringTag];
-assert.sameValue(toString.call(map), defaultTag);
+assert.sameValue(toString.call(map), '[object Object]');
 
 var mapIter = map[Symbol.iterator]();
 var mapIterProto = Object.getPrototypeOf(mapIter);
+assert.sameValue(toString.call(mapIter), '[object Map Iterator]');
 Object.defineProperty(mapIterProto, Symbol.toStringTag, {
   get: function() { return new String('ShouldNotBeUnwrapped'); },
 });
-assert.sameValue(toString.call(mapIter), defaultTag);
+assert.sameValue(toString.call(mapIter), '[object Object]');
 
 var set = new Set();
 delete Set.prototype[Symbol.toStringTag];
-assert.sameValue(toString.call(set), defaultTag);
+assert.sameValue(toString.call(set), '[object Object]');
 
 var setIter = set[Symbol.iterator]();
 var setIterProto = Object.getPrototypeOf(setIter);
+assert.sameValue(toString.call(setIter), '[object Set Iterator]');
 Object.defineProperty(setIterProto, Symbol.toStringTag, {value: false});
-assert.sameValue(toString.call(setIter), defaultTag);
+assert.sameValue(toString.call(setIter), '[object Object]');
 
 var wm = new WeakMap();
 delete WeakMap.prototype[Symbol.toStringTag];
-assert.sameValue(toString.call(wm), defaultTag);
+assert.sameValue(toString.call(wm), '[object Object]');
 
 var ws = new WeakSet();
 Object.defineProperty(WeakSet.prototype, Symbol.toStringTag, {value: 0});
-assert.sameValue(toString.call(ws), defaultTag);
+assert.sameValue(toString.call(ws), '[object Object]');
 
 delete JSON[Symbol.toStringTag];
-assert.sameValue(toString.call(JSON), defaultTag);
+assert.sameValue(toString.call(JSON), '[object Object]');
 
 var gen = (function* () {})();
 var genProto = Object.getPrototypeOf(gen);
 Object.defineProperty(genProto, Symbol.toStringTag, {
   get: function() { return {}; },
 });
-assert.sameValue(toString.call(gen), defaultTag);
+assert.sameValue(toString.call(gen), '[object Object]');
 
 var promise = new Promise(function() {});
 delete Promise.prototype[Symbol.toStringTag];
-assert.sameValue(toString.call(promise), defaultTag);
+assert.sameValue(toString.call(promise), '[object Object]');