serial_test.py

import serial
import sys

ser = serial.Serial('/dev/ttyUSB0', 115200, timeout = 2)  # open first serial port

print("Using", ser.portstr)       # check which port was really used

count = 0
while True:
    ser.write(b"PING\n")      # write a string
    reply = ser.readline()
    if reply != b"PING\n":
        print("UNEXPECTED RESPONSE after", count, "pings", reply)
        sys.exit(1)
    count += 1
    if count > 1000:
        print("Verified 1000 pings")
        count = 0

ser.close()