TARGET_OS_IPHONE and ApplicationTests

The simplest solution is to move the #import <Foundation/Foundation.h> statement out if the #if condition and replace Cocoa with AppKit like this:

#import <Foundation/Foundation.h>
#if TARGET_OS_IPHONE
   #import <UIKit/UIKit.h>
#else
   #import <AppKit/AppKit.h>
#endif

The Foundation umbrella header imports the NSObjCRuntime header which in turn imports the TargetConditionals header.

You need to add

#include <TargetConditionals.h>

source: https://opensource.apple.com/source/CarbonHeaders/CarbonHeaders-8A428/TargetConditionals.h.auto.html