I’m working on breaking components out of my Swift project into local SPM packages. I’m really starting to like the architecture. But I’m having trouble with testing. I’d like to ⌘-T in Xcode and run both the app unit tests and the SPM tests, but I can’t make it work. All the posts online redirect back to this answer: developer.apple.com/forums/th… But when I try to follow along, the SPM test targets just aren’t in the list. Anyone have a clue?

In general, I’m skeptical about AI code generation, especially in the hands of inexperienced engineers who think it’s smarter than they are. But when you need it to do a menial thing? Fantastic! For a Swift project, I needed a bunch of constants that I found on GitHub in a Python file. I pointed ChatGPT at the URL and asked it to generate the corresponding Swift enum, but change the keys from snake case to camel case. And… it just did it! I think it might even be right.

California Dreamin’ – WWDC 2023

It’s about a week before WWDC 2023 kicks off in sunny California, so here’s a list of things I’m hoping to see come out of Cupertino. I’m skipping the AR/VR stuff, since it’s been speculated ad nauseam. I’m sure it’ll be cool and awesome and weird and probably not cheap. And maybe it’ll make me dizzy

TLDR; Better Xcode, Better Siri, Better Mac Catalyst


Mostly, I just want Xcode to be better. Don’t crash. Don’t be slow. Is that too much to ask?

SPM Handling

We’ve all seen it. Switch branches, hit build and be faced with

Build operations are disabled: Package loading in progress. Please try again later.

I spend a lot of time working on Callisto, which is kind of a big app. We have dependencies split out into frameworks and it can take SPM a while to resolve all the packages when switching branches. So I hit this quite a lot. Usually, Xcode does a great job of queueing up actions when it’s busy. Like if you do a clean build and then run unit tests, it will finish the clean and then do the testing. That’s all I want for SPM resolution.

Better SwiftUI Tooling

I haven’t written a lot of SwiftUI. We toyed with it early on building Callisto, but it wasn’t ready for a big project like that. A couple months ago, we thought about trying to build a screen here or there with SwiftUI, but ran into roadblocks. One of the key features of SwiftUI is the live preview. To make those work, Xcode compiles bits of your code behind the scenes and shows them in preview pane. Callisto is a Catalyst app but has an AppKit plugin for doing Mac system things. Xcode could not handle that when trying to make a SwiftUI preview. Xcode would try to compile the AppKit code with UIKit and become very upset when it didn’t work. That left our foray into SwiftUI dead in the water.

Siri for Xcode

I’ve dabbled a bit with ChatGPT as a coding assistant. It’s great for small tasks with fiddly parameters. For instance, I needed to get the timestamp of some files. That’s the kind of thing that’s straightforward, but you don’t do it often, so you have to look up the specific API to stat the file and which attributes correspond to the creation date / modification date, etc. ChatGPT spit that code right out and I could move on to other things. But there’s friction there and the opportunity for a bespoke Xcode experience. I’m cautiously optimistic Apple will do something in this space, but I’m afraid it won’t be groundbreaking. Because, you know… Siri.

Catalyst and iOS Updates

Since Callisto is built with Mac Catalyst, these are the sorts of updates we’d love to see as developers.

Dynamic Type on Mac

Dynamic Type on iOS has been around for 10+ years. That’s the bit in iOS Settings that lets you make the text on your device a little bigger or a lot bigger than standard. All the apps that support Dynamic Type will pick up the change and text across the whole device changes size. That’s great! A boon for aging eyes everywhere.

But it isn’t supported at all on macOS. This recent announcement about new accessibility features coming in iOS 17 mentions

For users with low vision, Text Size is now easier to adjust across Mac apps such as Finder, Messages, Mail, Calendar, and Notes.

That sounds a lot like Dynamic Text on the Mac, so fingers crossed.

Auxiliary Window Replacement

Back in the day, lots of Mac apps used auxiliary windows that served as things like inspectors and floating tool panels. Apps like Photoshop had a bunch of these – paintbrushes, color panels, etc. You can still see these in AppKit apps like Preview and Quicktime Player, where the inspector is an auxiliary window. When you switch apps, it disappears to cut down on clutter. Right now, there’s nothing like that for Catalyst. The UIScene API for managing windows doesn’t have that level of distinction. Hopefully, at WWDC we’ll see a more mature Stage Manager implementation and at least some way of distinguishing main content windows and helper windows.

Multiple Processes on iOS

Callisto includes an embedded Python distribution for running the Jupyter Python Kernel. On the Mac, we just spawn a separate process and run Python normally. On iPad, we use a heavily modified Python to run in the same process space as the app to comply with App Store requirements. In practice, that hamstrings Callisto on the iPad a great deal. With a renewed interest in Pro apps on the iPad, it’d be incredible if we were allowed to run multiple processes and level the playing field between an M1 iPad and an M1 MacBook.

Yeah, never going to happen.

Other Stuff


A lot of folks have called for a dedicated Passwords app instead of burying password management in Settings. I’m all for that, but I’d also love to see password sharing via your Apple Family. That’s really the last feature I’d need to leave 1Password behind. 1Password has been fantastic, but they’ve really pivoted to a corporate focus, so they’re less of good fit when I just want to share the Netflix password with my family. (Only for persons in my immediate family, residing in the same household. Netflix, if you’re reading this, I promise.)

HKSV Streaming API

I’m pretty heavily invested in the HomeKit ecosystem and I’m mostly happy with it. (I’m looking at you Siri.) I’ve got several third party apps that will stream video from my cameras, but they can only show live feeds. HKSV (HomeKit Secure Video) records events from these cameras and saves to iCloud, but scrolling back through time is only available via Apple’s Home app. Third party apps aren’t able to access the history of clips because there’s just no API for it. With HomeKit (hopefully) maturing a little more this year, Apple should make that available to developers.

Better Siri for Mac

Yes, macOS has Siri. But as underwhelming as Siri is on iOS, it’s worse on Mac.

In my notes, I wrote down “Not Brain Dead”. Siri just fails at the most basic things sometimes. When I try to open an app in my Applications folder with the phrase “Open AppName”, it fails maybe 2 out of 3 times. I’m not sure why it’s so bad and I don’t know of any way to debug it.

I usually use my laptop with the lid closed with external monitor, keyboard, webcam, etc. That means I can’t use “Hey Siri” for security reasons. I agree being able to turn off an always-on microphone is important, but if Siri is a serious feature, why can’t I explicitly grant permission for Siri to listen with an external microphone? It is interesting to note that “Hey Siri” does work with the ($1600) Mac Studio Display. That’s attributed to the onboard A13 chip.

Another bit of low hanging fruit for Siri is menu commands. At least it seems low hanging to me. If I’m using an app like Xcode, that has a menu command called ‘Build’, I would expect Siri to understand if I said “Hey Siri, Build”. But like the double meat burger, Siri is strictly off the menu.

But the real dream is a conversational Siri. We’ve all seen Iron Man. We’ve seen Tony talking to Jarvis like a person as he works. Could Siri ever do that in the context of Xcode? Playing with ChatGPT has teased this kind of reality. “Write a method to delete all the files in a given directory.” That’s a thing ChatGPT can do in a web browser window. Why can’t Siri to do that in Xcode? Imagine an Apple trained LLM that especially knew about Swift, UIKit, and all the Apple technologies. Add in the context of the project you’re currently working on. Talk about a developer accelerant. But that’s a big leap, so it’s doubtful we’ll see that this year, but maybe the first step?

Things We Won’t See at WWDC

Apple Silicon Mac Pro

Apple announced Apple Silicon for Mac at WWDC of 2020, three years ago, and the first commercial M1 Macs shipped in November of 2020. At the time, Apple estimated that the transition to Apple Silicon would take about two years. It’s been two and a half years since that first M1 MacBook Air shipped but the Mac Pro still sports an Intel chip. Something has clearly run amok.

But the rumor mill is pretty quiet on the Mac Pro front. Usually at this point, there would be at least some mention of the debut of a high profile, flagship Mac. It seems like we’ll be waiting until later in the year to see what kind of behemoth you can build out of lots of iPhone chips.

HomePod + AppleTV

Years ago, HomePod ran its own fork of iOS called AudioOS. Apple merged AudioOS with tvOS several revisions back so now both these home devices run tvOS. Because they do similar things – played media and power HomeKit – that makes a lot of sense. But the two devices remained separate at a hardware level – a smart speaker and a TV streamer. I’ve been waiting for the hybrid devices for years now. There’s the HomePod with a screen, like an Amazon Echo Show, that does HomePod things, but augmented with a display. And there’s the AppleTV with a mic and speaker. The mic let’s you talk to the TV without holding the button on the remote and the speaker acts as a center channel for multiple HomePod sound stage.

Those are both consumer products, so not the kind of thing they’d squeeze into the WWDC Keynote, especially with the AR/VR announcement, but maybe this fall, just in time for Christmas.

Will we see any of this at WWDC? I certainly hope so. But there’s only one way to find out.

No sleep ‘til DubDub!

Better App Launching with SwiftUI for Unit Tests

TL;DR -- In SwiftUI, use a fake testing `App` instead of your real `App` 
to make sure you're actually testing your code. 

For unit testing, test coverage is an important metric. How much of your code base are you exercising during unit tests? Xcode is, unfortunately, not too bright when it comes to measuring coverage. It doesn’t have the intelligence to know if you’re “testing” a line of code, just that the line of code was executed. This is a problem right off the bat.

I’ve got a new app project in Xcode. The app does a little and I want to start adding tests before it gets too big. So I add a unit test target and Xcode plops in some empty tests. I run the unit tests, and they all pass since they’re empty. I check the coverage and it’s at 36%! How can that be, I didn’t test anything?

Xcode, the blissful idiot, is really reporting that 36% of the code was executed while running the unit tests. Usually, when an app starts up, it does some bootstrapping. You might set up your persistent storage, draw a couple of Views on screen, and maybe talk to the network. Xcode counts all that as “testing” because it ran during a unit test.

To make the test coverage more accurate, we need to do as little as possible outside of our actual unit tests. Jon Reid has a write-up of how to do this with a UIKit app by swapping out the app delegate during tests. But SwiftUI introduces a whole new startup sequence so we need a new approach for SwiftUI’s new app lifecycle.

After some futzing around, turns out it’s easy!

struct TestApp: App {					// 1
    var body: some Scene {
        WindowGroup {
            Text("I'm running tests!")

@main										// 2
struct TestDriver {
    static func main() {
        if NSClassFromString("XCTestCase") != nil {    // 3
        } else {

There are three key points that make this work:

  1. We need a dummy `App` struct to use instead of the real app. This simple stand-in circumvents all your usual app startup machinery. Instead of all the normal bootstrapping, we'll just get a window with the text "I'm running tests!".
  2. Remove the `@main` from your `App` implementation and add it here to `TestDriver`. Swift uses `@main` to figure out how to start your app. The `App` protocol provides a default implementation that, according to the docs, 'manages the launch process in a platform-appropriate way'. But by inserting our own wrapper layer here around, we can control _which_ `main()` is called.
  3. That brings us to the final point, use the good old `NSClassFromString` to decide if the testing bundle has been injected into our process. `XCTestCase` is only available during testing, so this is a reliable way to decide if unit testing is underway. Based on that, we can call the `main` method of either our real app or our testing stand-in. It turns out that the default implementation of `main` knows to use its parent struct to bootstrap the SwiftUI app.

Now when I run unit tests, my coverage is at 0.8%! That’s more like it. In order to boost my test coverage, I now have to actually test code. And the code coverage metric really starts to mean something.

Unit testing with UIDocumentPickerViewController – An Un-Googlable Bug

TLDR – If your unit tests crash with DocumentManager service tried to send a message to a deallocated host proxy, make sure you’re dismissing any presented instance of UIDocumentPickerViewController.

In our Callisto Xcode project, we’ve got a lot of unit tests. Like over a thousand. We’re at the point where if tests have a 0.1% chance of failing, then it happens every time. Our tests need to be really rock solid, or there’s no way we’ll get a clean run which is the only way CI will let a build through.

Some time ago, we started noticing the occasional test failure with an uncaught exception:

DocumentManager service tried to send a message to a deallocated host proxy

It would crop up when running test both locally and in CI. With so many tests, we get the weird edge case now and then, but they’re not worth the time to track down. We ignored it. With the recent update to Xcode 14.3 and macOS 13.3, the DocManager exception went from occasional annoyance to ‘omg, this happens every time I unit test on iOS’. So now we have to fix it.

But what’s a DocManager? IDK – there’s nothing with that name in our code and nothing in the docs about an Apple framework called DocManager. Looking through the traceback, it’s pretty obvious that it’s some kind of internal Apple thing. Surprisingly, a Google search for this error returns absolutely no results. That’s never a good sign.

But what’s a DocManager do? Callisto is UIDocument based, so maybe DocManager manages documents? A bunch of the unit tests open instances of a UIDocument and aren’t 100% about cleaning those up, so maybe some housekeeping will help. Cue the plumbing montage. We added a some bookkeeping to make sure that any open UIDocuments were closed at the end of each test, so now we’re sure there are no dangling UIDocuments. No impact – still the DocManager throws the exception.

This particular problem is a huge pain to track down. Somewhere in the tests, things get into a bad state. Later, while another test is running, some background thread discovers the bad state and throws an exception. The cause of the crash and the actual crashing are quite loosely coupled, making it hard to pin down the culprit. It also means that the offending tests will run just fine by itself, but only cause a crash when a large number of tests run, giving the background issue time to percolate to the surface.

After a couple hours of testing the tests and narrowing down which ones fail, it started to look like UIDocumentPickerViewController might be involved. We’ve got some ViewControllers that open a docPicker and get feedback via the docPicker’s delegate methods. To test those, we programmatically tap a button to cause the dockPicker to be presented, get a handle to that docPicker and call the delegate with the docPicker and some fake results. This works great for testing! Except for that pesky exception that gets thrown now and then.

If we take a closer look at the exception, we’ll see there’s a little more info attached in the userInfo dict, specifically a file and line number, DOCRemoteViewControlller.m line 42. Not that we have access to the source, but the name of the file, “Remote View Controller”, does offer a hint of its purpose. Those docPicker view controllers offer our app an escape hatch out of the sandbox and into the rest of the file system on the device. In my limited understanding, the docPickers interface with a separate process that manages file system access, so they actually represent some state from another (remote) long lived process. In the end, these dangling, un-dismissed docPickers were the root of the problem. Make sure all your UIDocumentPickerViewControllers are dismissed properly and the problem goes away.