Add string primitive test

test/built-ins/Object/getOwnPropertyDescriptor/primitive-string.js

@@ -0,0 +1,37 @@
+// Copyright (C) 2020 Alexey Shvayka. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-object.getownpropertydescriptor
+description: >
+  String primitive as first argument is coerced to object.
+info: |
+  Object.getOwnPropertyDescriptor ( O, P )
+
+  1. Let obj be ? ToObject(O).
+  [...]
+  3. Let desc be ? obj.[[GetOwnProperty]](key).
+  4. Return FromPropertyDescriptor(desc).
+
+  String Exotic Objects
+
+  String exotic objects always have a data property named "length" whose value is the number
+  of code unit elements in the encapsulated String value. Both the code unit data properties
+  and the "length" property are non-writable and non-configurable.
+---*/
+
+assert.sameValue(Object.getOwnPropertyDescriptor('', '0'), undefined);
+
+var indexDesc = Object.getOwnPropertyDescriptor('foo', '0');
+
+assert.sameValue(indexDesc.value, 'f', '[[Value]]');
+assert.sameValue(indexDesc.writable, false, '[[Writable]]');
+assert.sameValue(indexDesc.enumerable, true, '[[Enumerable]]');
+assert.sameValue(indexDesc.configurable, false, '[[Configurable]]');
+
+var lengthDesc = Object.getOwnPropertyDescriptor('foo', 'length');
+
+assert.sameValue(lengthDesc.value, 3, '[[Value]]');
+assert.sameValue(lengthDesc.writable, false, '[[Writable]]');
+assert.sameValue(lengthDesc.enumerable, false, '[[Enumerable]]');
+assert.sameValue(lengthDesc.configurable, false, '[[Configurable]]');