text: """
  Used with ble_uart_echo_test.py. Transmits "echo" to the UARTService and receives it back.
  """
  
  import time
  
  from adafruit_ble import BLERadio
  from adafruit_ble.advertising.standard import ProvideServicesAdvertisement
  from adafruit_ble.services.nordic import UARTService
  
  ble = BLERadio()
  while True:
      while ble.connected and any(UARTService in connection for connection in ble.connections):
          for connection in ble.connections:
              if UARTService not in connection:
                  continue
              print("echo")
              uart = connection[UARTService]
              uart.write(b"echo")
              # Returns b'' if nothing was read.
              one_byte = uart.read(4)
              if one_byte:
                  print(one_byte)
              print()
          time.sleep(1)
  
      print("disconnected, scanning")
      for advertisement in ble.start_scan(ProvideServicesAdvertisement, timeout=1):
          if UARTService not in advertisement.services:
              continue
          ble.connect(advertisement)
          print("connected")
          break
      ble.stop_scan()
  