UIViewControllers should also be tested. But tests for the connection of two controllers via Storyboard segues are often missing. Here a example how you can test segue from one to another UIViewController via -(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender with OCMock.

Test segue between two UIViewControllers

UIViewController *vc = // ViewController
id mockVC = [OCMockObject partialMockForObject:vc];
UIButton *button = // Button on view of ViewController

UIStoryboardSegue *storyBoardSegue = [OCMArg checkWithBlock:^BOOL(id obj){
    UIStoryboardSegue *segue = obj;
    
    UIViewController *src = segue.sourceViewController;
    UIViewController *dst = segue.destinationViewController;
    NSString *idtf = segue.identifier;
    
    bool isCorrectSrcController = [src isKindOfClass:[SRCViewController class]]; // replace type
    bool isCorrectDstController = [dst isKindOfClass:[DSTViewController class]]; // replace type
    bool isCorrectSegueIdentifier = [idtf isEqualToString:@"IDENTIFIER"]; // replace identifier
    
    return isCorrectSrcController && isCorrectDstController && isCorrectSegueIdentifier;
}];

[[mockVC expect] prepareForSegue:storyBoardSegue sender:button];

// simulate button clock
[button sendActionsForControlEvents:UIControlEventTouchUpInside];

[mockVC verify];