iOS deep linking with Xcode UI testing

I want to test parts of my app UI in isolation, so avoid having to drill down from the splash screen to the pages in question. My app implements deep linking, but I can't figure out how to configure XCUIApplication in the setUp() to trigger the page transition.

I have a method in the app delegate called openURL() which handles this for the production app. It works great, but when I call it (below), nothing happens. If I put a breakpoint in openURL() it never even gets hit.

    override func setUp() {
        super.setUp()
        continueAfterFailure = false

        XCUIApplication().launch()
      
        guard let url = NSURL(string: "fooapp://page/3") else {
            fatalError("Couldn't create URL")
        }


        UIApplication.sharedApplication().openURL(url)
    }

What I really want is to set UIApplicationLaunchOptionsURLKey in launchOptions and just let the app behave as if it received an external URL. I see launchArguments and launchEnvironment are available on XCUIApplication, but then I have to write something special to extract those values out and manually call openURL somewhere in the app delegate. What's the right way to do this?