UserDefaults.standard.addObserver calling observeValueForKeyPath multiple times

KVOProblem.swift

import Cocoa

let testKey: String = "TESTKEY"
let defaults: UserDefaults = UserDefaults.standard

// Remove Perferences & register default
defaults.removePersistentDomain(forName: Bundle.main.bundleIdentifier!)
defaults.register(defaults: [testKey : false])

class testClass: NSObject {
    var callCount: Int = 0
    override init() {
        super.init()
        defaults.addObserver(self, forKeyPath: testKey, options: .new, context: nil)
    }
    
    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        self.callCount += 1
        print("Hello World: (\(self.callCount)times)")
    }
}

let testObj = testClass()
defaults.set(true, forKey: testKey)

Thx for Replying!