How to let the app know if it's running Unit tests in a pure Swift project?

One annoying thing when running tests in Xcode 6.1 is that the entire app has to run and launch its storyboard and root view controller. In my app this runs some server calls that fetches API data. However, I don't want the app to do this when running its tests.

With preprocessor macros gone, what's the best for my project to be aware that it was launched running tests and not an ordinary launch? I run them normally with command + U and on a bot.

Pseudocode:

// Appdelegate.swift
if runningTests() {
   return
} else {
   // do ordinary api calls
}

Instead of checking if the tests are running to avoid side-effects, you could run the tests without the host app itself. Go to Project Settings -> select the test target -> General -> Testing -> Host Application -> select 'None'. Just remember to include all files you need to run the tests, as well as libraries normally included by the Host app target.