fatuhoku / HSPTestableSegue

A Objective-C category that helps you structure your iOS UIViewControllers' prepareForSegue:sender: code in a testable way

HSPTestableSegue

A Objective-C category that helps you structure your iOS UIViewControllers' prepareForSegue:sender: code in a testable way.

Usage

If you use Storyboards, you're probably going to have UIViewController subclasses whose prepareForSegue:sender: method looks a bit like this:

// YOURSourceViewController.m
...
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if ([segue.identifier isEqualToString:@"seg_untestable_segue"]) {
        YOURSpecificViewController *viewController = segue.destinationViewController;
        // Do something with the destination View Controller
        viewController.model = [self launchTheNukes];
    } else if ([segue.identifier isEqualToString:@"seg_another_untestable_segue"]) {
        YOURDestinationViewController *viewController = segue.destinationViewController;
        // Do something else with this destination View Controller...
        ...
    }
    ...
}
...

This is the vital glue that links one screen of your application to the next: and yet, written like this, it's notoriously difficult to test and to verify the behaviour of. Your options are:

• supply a mock UIStoryboardSegue, whose behaviours need to be set up to return various destinationViewControllers
• actually fire up the app and physically invoke the segue

With HSPTestableSegue you can write the same code like this:

// YOURSourceViewController.m
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    [self prepareForSegueWithSeguePreparationBlocks:segue sender:sender];
}

+ (NSDictionary *)seguePreparationBlocks {
    return @{
            @"seg_testable_segue":^(YOURSourceUIViewController *source,
                                    YOURDestinationUIViewController *destination,
                                    id sender) {
                // Do something with the source and destination View Controller
                destination.model = source.property;
            }
    };
}

Here, we've effectively split up the implementation of prepareForSegue:sender: into a dictionary of segue preparation code blocks keyed on the segue identifier, supplied by the dictionary returned by seguePreparationBlocks.

This is made possible by implementing a small category on UIViewController that implements methods like prepareForSegueWithSeguePreparationBlocks:sender:. This method replaces the conditional block and looks up the appropriate code block by using the segue identifier.

With the blocks separately defined, there's another method called prepareForSegueWithIdentifier:destinationViewController: that's intended to let you inject a mock View Controller into the segue preparation code block, so that you can verify its behaviour.

    YOURSourceUIViewController *viewController = [[YOURSourceUIViewController alloc] init];
    id mockViewController = mock([YOURDestinationUIViewController class]);   // create a mock here

    [viewController prepareForSegueWithIdentifier:@"seg_very_testable_segue"
                        destinationViewController:mockViewController];   // pretend you're about to perform the segue

    [MKTVerify(mockViewController) setModel:source.property];   // verify behaviour (here, OCMockito is used)

If you're unsure on anything, a demo project has been included. To run the included test, you'll need Cocoapods to download OCMockito like so:

cd TestableSegueDemo
pod install
open TestableSegueDemo.xcworkspace

And just hit Cmd+U.

If in doubt, just read the code. There's not a huge amount of it =]

Installation

Just copy Source/UIViewController+TestableSegues.{h,m} into your project and start using them right away away.

Contributing

I'd love to hear what you think of this approach to making segue preparation code more testable. Feedback welcome! Any questions or problems, just open a new issue and I'll get back to you.

License

MIT