If your Unit Tests break, be sure to check out this link.
It usually means there's a non-included Pods configuration set in your Debug build. Be sure to scroll down for further information if you really need to look.
It might also be helpful to reference the Podfile depency declarations page just in case you've got to do some Podfile (or Pod) hacking.
Finally, don't forget to make sure the libPods.a file is added as a linked library to the Unit Tests bundle. That could cause problems too if it isn't.
Where would I do this 'Finally, don't forget to make sure the libPods.a file is added as a linked library to the Unit Tests bundle. That could cause problems too if it isn't.'