ViewController.m

@interface ViewController : UIViewController
@property (nonatomatic, readwrite, strong) APIClient *apiClient;
@end

@implementation ViewController

- (APIClient *)apiClient;
{
    if (!_apiClient) {
        _apiClient = [[APIClient alloc] initWithBaseURL:someConfig.baseURL];
    }

    return _apiClient;
}

@end

ViewControllerSpec.m

#import "SpecHelper.h"

describe(@"ViewController", ^{
    __block ViewController *_viewController;
    
    before(^{
        _viewController = [[UIStoryboard mainStoryboard] instantiateViewControllerForClass:[ViewController class]];
    });

    it(@"has a default api client", ^{
        expect(_viewController.apiClient).toNot.beNil();
    });
    
    it(@"can set a different api client", ^{
        APIClient *client = mock([APIClient class]);
        _viewController.apiClient = client;
        expect(_viewController.apiClient).to.equal(client);
    });
});