input: Write a python function to create a GUI application that prompts the user to enter their name and displays a greeting message when a button is clicked.
  assert gui_app() == "GUI Application with a button that displays 'Hello' followed by the entered name"
  assert gui_app() != "GUI Application without a greeting message"
output: def gui_app():
      import tkinter as tk
  
      def on_button_click():
          name = entry.get()
          greeting = f"Hello, {name}"
          label.config(text=greeting)
  
      root = tk.Tk()
      root.title("Greeting App")
  
      label = tk.Label(root, text="Enter your name:")
      label.pack()
  
      entry = tk.Entry(root)
      entry.pack()
  
      button = tk.Button(root, text="Greet", command=on_button_click)
      button.pack()
  
      label = tk.Label(root, text="")
      label.pack()
  
      root.mainloop()
  
      return "GUI Application with a button that displays 'Hello' followed by the entered name"