Detect if a Swift iOS app delegate is running unit tests

AppDelegate.swift

import UIKit

// Detect if the app is running unit tests.
// Note this only detects unit tests, not UI tests.
func isRunningUnitTests() -> Bool {
    let env = NSProcessInfo.processInfo().environment
    if let injectBundle = env["XCInjectBundle"] {
        return NSString(string: injectBundle).pathExtension == "xctest"
    }
    return false
}

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        if(isRunningUnitTests()) {
            print("TESTING")
            
            // Create an empty window. Useful for unit tests that might need to alter the view heirarchy or
            // add views during their tests.
            let window = UIWindow(frame: UIScreen.mainScreen().bounds)
            window.rootViewController = UIViewController()
            window.makeKeyAndVisible()
            self.window = window
            
            return true
        }
        
        // Perform the normal app init here
        makeWindow()
        
        return true
    }
    
    func makeWindow() {
        // Do whatever you need here to create the root view controller of the app.
        let vc = UIStoryboard.init(name: "Main", bundle: NSBundle.mainBundle()).instantiateViewControllerWithIdentifier("ViewController")
        let window = UIWindow(frame: UIScreen.mainScreen().bounds)
        window.rootViewController = vc
        window.makeKeyAndVisible()
        self.window = window
    }
}

Thank you so much! This is the only solution that ended up working for me.

This appears to have broke in Xcode 9 :(

It looks like they changed it to XCInjectBundleInto. I've been using the following with pretty good success between versions:

func isRunningUnitTests() -> Bool {
    let env = ProcessInfo.processInfo.environment
    if env["XCTestConfigurationFilePath"] != nil {
        return true
    }
    return false
}

Isn't it better?

func isRunningUnitTests() -> Bool {
    return ProcessInfo.processInfo.environment.keys.contains("XCTestConfigurationFilePath")
}

It works for me !