Adding tests for the fixes in ArraySetLength().

Author: iamstolis

graal-js/src/com.oracle.truffle.js.test/js/GR-24687.js

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2020, 2020, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * Licensed under the Universal Permissive License v 1.0 as shown at http://oss.oracle.com/licenses/upl.
+ */
+
+load('assert.js');
+
+// valueOf() should be invoked twice (from ToUint32() and ToNumber())
+var valueOfCalls = 0;
+Object.defineProperty([0, 1, 2], 'length', {
+    value: {
+        valueOf: function () {
+            valueOfCalls++;
+            return 3;
+        }
+    }
+});
+assertSame(2, valueOfCalls);
+
+// length should remain writable when its re-definition is refused
+var array = [42, 211];
+assertThrows(function () {
+    Object.defineProperty(array, 'length', {
+        writable: false,
+        configurable: true
+    });
+}, TypeError);
+array.length = 5;
+assertSame(5, array.length);
+
+// length should be constant after re-definition with "writable: false"
+var array = [0, 1, 2];
+Object.defineProperty(array, 'length', {
+    value: 3,
+    writable: false
+});
+assertThrows(function () {
+    array.splice(1, 2, 4);
+}, TypeError);
+assertSame(3, array.length);
+assertSame(array[0], 0);
+assertSame(array[1], 4);
+assertSame(array[2], undefined);
+
+true;