ember qunit needs unknown controller factory

I have this test for a controller; it is using ember-flash-message controller:

moduleFor 'controller:about', 'About Controller', {
    needs: ['controller:flashMessage']
}

But I get this error:

Setup failed on exists: Attempting to register an
 unknown factory: `controller:flashMessage`

I am sure I included the FlashMessageController. Why do I get this error?