There's a flaw in the test here. You need to specify an input type in order for the merge order to work correctly; otherwise, a normal `Input` will be created, and the `FileInput` settings merged to it, which will result in the wrong context.

That said, even with `'type' => 'Zend\InputFilter\FileInput'` in your configuration, you still get an error -- just a different one (duplicated filters).