Move test and actually call it

Author: Girgias

Zend/tests/type_declarations/union_types/standalone_null.phpt renamed to Zend/tests/type_declarations/standalone_null.phpt

@@ -3,9 +3,14 @@ Null can be used as a standalone type
 --FILE--
 <?php
 
-function test(): null {}
+function test(null $v): null {
+    return $v;
+}
+
+var_dump(test(null));
 
 ?>
 ===DONE===
 --EXPECT--
+NULL
 ===DONE===