Add Object.assign test

test/built-ins/Object/assign/strings-and-symbol-order-proxy.js

@@ -0,0 +1,41 @@
+// Copyright (C) 2020 Alexey Shvayka. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-object.assign
+description: >
+  Proxy keys are iterated in order they were provided by "ownKeys" trap.
+info: |
+  Object.assign ( target, ...sources )
+
+  [...]
+  4. For each element nextSource of sources, in ascending index order, do
+    a. If nextSource is neither undefined nor null, then
+      [...]
+      ii. Let keys be ? from.[[OwnPropertyKeys]]().
+      iii. For each element nextKey of keys in List order, do
+        1. Let desc be ? from.[[GetOwnProperty]](nextKey).
+
+  [[OwnPropertyKeys]] ( )
+
+  [...]
+  7. Let trapResultArray be ? Call(trap, handler, « target »).
+  8. Let trapResult be ? CreateListFromArrayLike(trapResultArray, « String, Symbol »).
+  [...]
+  23. Return trapResult.
+features: [Proxy, Symbol]
+includes: [compareArray.js]
+---*/
+
+var getOwnKeys = [];
+var ownKeysResult = [Symbol(), "foo", "0"];
+var proxy = new Proxy({}, {
+  getOwnPropertyDescriptor: function(_target, key) {
+    getOwnKeys.push(key);
+  },
+  ownKeys: function() {
+    return ownKeysResult;
+  },
+});
+
+Object.assign({}, proxy);
+assert.compareArray(getOwnKeys, ownKeysResult);