content: from dash import Dash, Input, Output, html, callback, ALL
  
  from tests.background_callback.utils import get_background_callback_manager
  
  background_callback_manager = get_background_callback_manager()
  handle = background_callback_manager.handle
  
  app = Dash(__name__, background_callback_manager=background_callback_manager)
  
  app.layout = html.Div(
      [
          html.Button(id={"type": "run-button", "index": 0}, children="Run 1"),
          html.Button(id={"type": "run-button", "index": 1}, children="Run 2"),
          html.Button(id={"type": "run-button", "index": 2}, children="Run 3"),
          html.Div(id="result", children="No results"),
      ]
  )
  app.test_lock = lock = background_callback_manager.test_lock
  
  
  @callback(
      Output("result", "children"),
      [Input({"type": "run-button", "index": ALL}, "n_clicks")],
      background=True,
      prevent_initial_call=True,
  )
  def update_output(n_clicks):
      found = max(x for x in n_clicks if x is not None)
      return f"Clicked '{found}'"
  
  
  if __name__ == "__main__":
      app.run(debug=True)
  