How do you make the sender display name appear with JSQMessageViewController?

I have the following function that gets called for adding a message:

    func addMessage(text: String, displayName: String) {
        let message = JSQMessage(senderId: "tester", displayName: displayName, text: text)
        messages.append(message)

        finishReceivingMessage()

}

Then in this function

    override func collectionView(collectionView: JSQMessagesCollectionView!,
    messageDataForItemAtIndexPath indexPath: NSIndexPath!) -> JSQMessageData! {
        return messages[indexPath.item]
}

I return the message date for that indexPath. The message appears correctly but there is no display name.