Commerce module: Why this commerce_order_ui_form_commerce_order_ui_order_form_alter won't work?
I'm guessing by your rep that you already know most of the following but it pays to check:


Hooks can only exist once per module
Hooks must begin with the module name


So this means commerce_order_ui_form_commerce_order_ui_order_form_alter(&amp;$form, &amp;$form_state) won't work inside username_check.module

If you really want to put the code inside the username_check module call it:

username_check_form_commerce_order_ui_order_form_alter(&amp;$form, &amp;$form_state)



[edit:]

Of course, you shouldn't put test code inside an existing module.  The best way to test code is to make your own custom module, which is pretty easy once you get the hang of it.