Do not use dynamic property

tests/ExporterTest.php

@@ -58,7 +58,6 @@ final class ExporterTest extends TestCase
 
         $storage = new SplObjectStorage;
         $storage->attach($obj2);
-        $storage->foo = $obj2;
 
         $resource = fopen('php://memory', 'r');
         fclose($resource);
@@ -147,11 +146,10 @@ EOF
             'export splObjectStorage' => [$storage,
                 <<<'EOF'
 SplObjectStorage Object #%d (
-    'foo' => stdClass Object #%d (
-        'foo' => 'bar',
-    ),
     'Object #%d' => Array &0 [
-        'obj' => stdClass Object #%d,
+        'obj' => stdClass Object #%d (
+            'foo' => 'bar',
+        ),
         'inf' => null,
     ],
 )