Yeah probably. I've always run it from my real machine, however I've never tried TDD yet. I can imagine this will be an issue if one of my tests needs mcrypt.... but anyways try running it on the real machine and post the errors. I can imagine that perhaps growl doesn't work in the VM but I may be entirely wrong. Also, I doubt it but maybe running npm install notify-send will fix the issue.
If you're running gulp from within the Homestead environment, it'll fail to notify because there's no notification system in the command line by default and it has no way of sending the notifications remotely to your computer i.e. outside of the homestead environment.
It's essentially letting you know that it tried to send a notification, but failed. On the host machine it works as it sends the notification via the native notifications system.