input: Write a python function to create a simple Tkinter application with a button that updates a label when pressed.
  assert app.btn.cget("text") == "Press me"
  assert app.label.cget("text") == ""
  app.on_press()
  assert app.label.cget("text") == "You pressed the button!"
output: import tkinter as tk
  
  class App:
      def __init__(self, root):
          self.root = root
          self.root.title("Simple Tkinter App")
          
          self.label = tk.Label(root, text="")
          self.label.pack()
          
          self.btn = tk.Button(root, text="Press me", command=self.on_press)
          self.btn.pack()
  
      def on_press(self):
          self.label.config(text="You pressed the button!")
  
  def create_app():
      root = tk.Tk()
      app = App(root)
      root.mainloop()
      return app