Action of StatusItem not working in Swift

So I am a newbie to Swift and wanted to create a simple example status bar app on MacOS. To keep things clean I created a subclass App which is creating the status item. This class is then created in the applicationDidFinishLaunching function of the AppDelegate.swift.

But somehow nothing is printed on the console when I press the status icon. However if I copy the code in the AppDelegate file it works. Does someone know what I am doing wrong and why it is not working in the subclass?

Here is the code of my own class:

import Cocoa

class App: NSObject {

    let menuBarItem = NSStatusBar.system.statusItem(withLength: NSStatusItem.squareLength)

    override init() {
        print("created app instance");

        if let button = menuBarItem.button {
            button.image = NSImage(named: NSImage.Name("StatusBarButtonImage"))
            button.action = #selector(test(_:))
        }
    }

    @objc func test(_ sender: Any?) {
        print("button was pressed")
    }
}

and the AppDelegate:

import Cocoa

@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {

    var appInstance: App!

    func applicationDidFinishLaunching(_ aNotification: Notification) {
        // Insert code here to initialize your application
        appInstance = App()
    }

    func applicationWillTerminate(_ aNotification: Notification) {
        // Insert code here to tear down your application
    }
}