On rare occasions when running OS X desktop or iOS mobile tests, a Mac pop-up message will appear during your tests:

This computer's local hostname "Mac-x.local" is already in use on this network. The name has been changed to "Mac-x.local". 

This pop-up shouldn't affect the outcome of your test, and all the commands in the test should execute as expected.

The reason this pop-up occasionally occurs is due to a Mac/Bonjour error. For instance, our Mac virtual machines are given individual, unique hostnames. However, the Mac OS ignores them and uses the name “Mac” instead, and registers that name in the .local domain using Bonjour. Bonjour then has a mechanism which sets the Mac name to “Mac-2, Mac-3, etc”. 

Unfortunately, sometimes this mechanism fails, resulting in two Macs attempting to register the same name, simultaneously. When this failure happens, the second Mac encounters the pop-up error message.

Since this is a Mac/Bonjour error, there is not much action we can take on our end. On the bright side, this pop-up error message rarely happens, and shouldn't affect the outcome of your test. Your tests run normally in the background without interference since this is a system level non-intrusive notification.

Happy Automation Testing!