Testing in procedural programming code

I have designed and implemented, for my final year in college, an autonomous robot with Arduino board microcontroller. The robot wanders around an area, avoids obstacles and tries to detect intruders.

I have to do some testing for this project . Could anyone help me by telling what test procedures I can perform in procedural code?

Observation of the behavior of robot could be one of them?

Servo servoLeft;          // Define left servo
Servo servoRight;         // Define right servo
const int trigPin = 5;
const int echoPin = 2;
int buzzerPin = 6;               // choose the pin for the LED //buzzer
int inputPin = 9;              // choose the input pin (for PIR sensor)

int val = 0;  
Timer t;
boolean pirSense = false;
long xronos=0;

void setup() { 
Serial.begin(9600);
 servoLeft.attach(4);      // Set left servo to digital pin 10
 servoRight.attach(3);     // Set right servo to digital pin 9

 pinMode(buzzerPin, OUTPUT);      // declare LED as output
 pinMode(inputPin, INPUT);     // declare sensor as input

 pinMode(trigPin, OUTPUT);
 pinMode(echoPin, INPUT);
 t.every(30000,monitoring);
  } 

  void loop() {  
  long duration, distance;
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  pinMode(echoPin, INPUT);
  duration = pulseIn(echoPin, HIGH);
  distance = microsecondsToCentimeters(duration);
   delay(100);
   Serial.println(distance);
   if (distance >= 40){
       moveForward();
     }
      else {

    stopMove();
    int x = random(0,2);  
    if(x == 0 ){ 
    turnRight();     
    delay(500);
   }
   else{
     turnLeft();       
    delay(500);
   }
  }
 t.update();
 }


 void monitoring(){
  xronos = now();
 while( xronos+5 >now() ){
  stopMove();
 delay(1000);
 pirSensor();
 }

}


  // Motion routines for forward, reverse, turns, and stop
  void reverse() {
  servoLeft.write(0);
 servoRight.write(180); 
 }

 void moveForward() {
 servoLeft.write(180);
 servoRight.write(0);
 }

  void turnRight() {
 servoLeft.write(180);
 servoRight.write(180);
  }
 void turnLeft() {
  servoLeft.write(0);
  servoRight.write(0);
  }

 void stopMove() {
 servoLeft.write(90);
 servoRight.write(90);
  }

 long microsecondsToCentimeters(long microseconds)
 {
 // The speed of sound is 340 m/s or 29 microseconds per centimeter.
 // The ping travels out and back, so to find the distance of the
 // object we take half of the distance travelled.
 return microseconds / 29 / 2;
 }