add test

Author: devnexen

ext/standard/tests/gh20840.phpt

@@ -0,0 +1,34 @@
+--TEST--
+GH-20840 (var_dump() crash with nested objects)
+--CREDITS--
+bendrissou
+--FILE--
+<?php
+class Node {
+    public $next;
+}
+
+$firstNode = new Node();
+$node = $firstNode;
+
+for ($i = 0; $i < 5000; $i++) {
+    $newNode = new Node();
+    $node->next = $newNode;
+    $node = $newNode;
+}
+
+try {
+    var_dump($firstNode);
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+
+while ($next = $firstNode->next) {
+    $firstNode->next = $next->next;
+}
+?>
+--EXPECTF--
+object(Node)#1 (1) {
+%a
+}
+Maximum call stack size of %d bytes (zend.max_allowed_stack_size - zend.reserved_stack_size) reached. Infinite recursion?