code: def test_dlfi001_download_file(dash_dcc):
      filename = "chuck.jpg"
      asset_folder = os.path.join(
          os.path.dirname(__file__), "download-assets"
      )
      # Create app.
      app = Dash(__name__, prevent_initial_callbacks=True)
      app.layout = html.Div(
          [html.Button("Click", id="btn"), dcc.Download(id="download")]
      )
  
      @app.callback(
          Output("download", "data"), Input("btn", "n_clicks")
      )
      def download(_):
          return dcc.send_file(os.path.join(asset_folder, filename))
  
      dash_dcc.start_server(app)
  
      # Check that there is nothing before clicking
      fp = os.path.join(dash_dcc.download_path, filename)
      assert not os.path.isfile(fp)
  
      dash_dcc.find_element("#btn").click()
  
      # Check that a file has been download, and that it's content matches the original.
      until(lambda: os.path.exists(fp), 10)
      with open(fp, "rb") as f:
          content = f.read()
      with open(os.path.join(asset_folder, filename), "rb") as f:
          original = f.read()
      assert content == original
  
      assert dash_dcc.get_logs() == []
  
label_desc: Use image node_id 1 for calling a global function with example usage: test_dlfi001_download_file(dash_dcc) and returns: dcc