Arduino IO SPEED TEST

int op=12;

void setup(){
  Serial.begin(9600);
  pinMode(op,OUTPUT);
 unsigned long int a=millis();
 for(int i=0;i<10000;i++){
  digitalWrite(op,LOW);
  digitalWrite(op,HIGH);
 }
 unsigned long int b=millis();
 unsigned long int c=b-a;
  Serial.print("Time Usage=");
    Serial.println(c);
}
void loop(){

}