Add tests for `Object.groupBy` and `Map.groupBy` with string items

test/built-ins/Map/groupBy/string.js

@@ -0,0 +1,22 @@
+// Copyright (c) 2023 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-map.groupby
+description: Map.groupBy works for string items
+info: |
+  Map.groupBy ( items, callbackfn )
+  ...
+includes: [compareArray.js]
+features: [array-grouping, Map]
+---*/
+
+const string = 'abcd';
+
+const map = Map.groupBy(string, function (char) {
+  return char < 'c' ? 'before' : 'after';
+});
+
+assert.compareArray(Array.from(map.keys()), ['before', 'after']);
+assert.compareArray(map.get('before'), ['a', 'b']);
+assert.compareArray(map.get('odd'), ['c', 'd']);

test/built-ins/Object/groupBy/string.js

@@ -0,0 +1,22 @@
+// Copyright (c) 2023 Ecma International.  All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-object.groupby
+description: Object.groupBy works for string items
+info: |
+  Object.groupBy ( items, callbackfn )
+  ...
+includes: [compareArray.js]
+features: [array-grouping]
+---*/
+
+const string = 'abcd';
+
+const obj = Object.groupBy(string, function (char) {
+  return char < 'c' ? 'before' : 'after';
+});
+
+assert.compareArray(Object.keys(obj), ['before', 'after']);
+assert.compareArray(obj['before'], ['a', 'b']);
+assert.compareArray(obj['after'], ['c', 'd']);