What's the conventional location for storing stub classes?

I have a system under test and I need to create some stub classes to isolate my SUT. I'm using NetBeans and my question is, should the test classes be saved in the test folder along with the test class or in the main package next to the stubee(?)?

I have heard some creating stubs as inner classes in the test class. I don't want to do that because a lot of my stubs will be shared among multiple classes, so it's better design to make them stand alone and I want to follow the convention of where they're usually stored.

Thanks.