only in patch2:
unchanged:
--- a/modules/simpletest/tests/common.test
+++ b/modules/simpletest/tests/common.test
@@ -1988,6 +1988,18 @@ class DrupalRenderTestCase extends DrupalWebTestCase {
 
     // The elements should appear in output in the same order as the array.
     $this->assertTrue(strpos($output, $second) < strpos($output, $first), 'Elements were not sorted.');
+
+    // The order of children with same weight should be preserved.
+    $element_mixed_weight = array(
+      'child5' => array('#weight' => 10),
+      'child3' => array('#weight' => -10),
+      'child1' => array(),
+      'child4' => array('#weight' => 10),
+      'child2' => array(),
+    );
+
+    $expected = array('child3', 'child1', 'child2', 'child5', 'child4');
+    $this->assertEqual($expected, element_children($element_mixed_weight, TRUE), 'Orders of Elemenets with same weights are kept.');
   }
 
   /**