Tip #1 for designers — you do not want to work with any company who ask you to work for free, for any reason.
Here’s what they should say. “We love your portfolio and would like to hire you for a stand alone project. So you know, there is potential for additional work beyond this project.”
People who ask you to work for free to “prove” yourself will bleed you dry in a thousand other little ways, even if they’re paying you.
There are times when working for free is okay. That’s not one of them.