if (player_test1.getWorld() != null)

public class Enemy_Test2 extends Animal
{
    //instance fields
    /**
     * Assigns SimpleTimer the variable of timer to this class.
     */
    private SimpleTimer timer = new SimpleTimer();
    /**
     * turnPhase is assigned to hold a boolean value
     */
    private boolean turnPhase;
    /**
     * phasteTimer is assigned to hold a numerical value of -1
     */
    private int phaseTimer = -1;
    /**
     * Actor is assigned to be the variable pursued
     */
    private Actor pursued;
    /**
     * obstacleTimer is assigned to hold a numerical value
     */
    private int obstacleTimer;
    /**
     * bulletTimer is assigned to hold a numerical value
     */
    private int bulletTimer;
    
    private boolean rangeOccur;
    
    public void act()
    {
        if (getObjectsInRange(650, Player_Test1.class).isEmpty() && los.obstructedView(this, pursued, Walls.class))
        {
            pursue();
        }   
        else
        {
            randomMovement();
        }
    }
    
    /**
     * Method summary: This method makes this class move forward at a randomly selected distance then to stop for a randomly selected amount of time only then to instantly turn a random amount of degrees to then stop for a randomly selected amount of time to only move foward again a randomly selected distance (loop). This method also able to detect when this class is in contact with a wall, if this class is in contact with a wall the class will turn away from the wall.
     */
    public void randomMovement()
    {
        // control code (when out of range of or path obstructed toward player)
        int sign = (int)Math.signum(phaseTimer); // '1' means moving or turning and '-1' means stopped after moving or turning
        phaseTimer -= sign; // step toward zero
        if (phaseTimer == 0)
        {
            if (sign == -1)
            {
                if (turnPhase) phaseTimer = 50+Greenfoot.getRandomNumber(400);
                else phaseTimer = 1;
                turnPhase = !turnPhase;
            }
            else
            {
                if (turnPhase) phaseTimer = -(50+Greenfoot.getRandomNumber(400));
                else phaseTimer = -(50+Greenfoot.getRandomNumber(30));
            }
        }
             
        if (sign > 0)
        {
            if (turnPhase) turn(Greenfoot.getRandomNumber(360)); else move(1);
        }

        if (atWorldEdge() || isTouching(Walls.class) || isTouching(BulletPassableWalls.class))
        {
            turn(160+Greenfoot.getRandomNumber(180)-90);
            
        }
         
        
    }
    
    /**
     * Method summary: This method will get the coordinates of the pursued (Player_Test1.class) and will continuously turn towards those coordinates and move foward at a move speed of 2 and will execute the shoot method. This method also able to detect when this class is in contact with a wall, if this class is in contact with a wall the class will turn away from the wall.
     */
    public void pursue()
    {
        int x = getX(), y = getY();
        turnTowards(pursued.getX(), pursued.getY());
        move(1);
        shoot();
        
        if (atWorldEdge() || isTouching(Walls.class))
        {
            turn(160+Greenfoot.getRandomNumber(180)-90);
        }
         
        if (isTouching(Walls.class) || isTouching(BulletPassableWalls.class))
        {
            setLocation(x, y);
        }
       
    }
    
    /**
     * This method will execute the shootBullet method every 360 milliseconds that elapse and will play the sound "Pistol Shot.mp3" every time this happens.
     */
    public void shoot()
    {     
        if (timer.millisElapsed() >= 360)
        {
            shootBullet();
            timer.mark();
            Greenfoot.playSound("Pistol Shot.mp3");
        }
    }
     
    /**
     * Method summary: This method spawns an Enemy_Bullet_Test1 class on this classes coordinates that is in the world and will rotate the Enemy_Bullet_Test1 class towards Player_Test1's coordinates.
     */
    public void shootBullet()
    {
        Enemy_Bullet_Test1 enemy_bullet = new Enemy_Bullet_Test1();
        enemy_bullet.setRotation(getRotation());
        getWorld().addObject(enemy_bullet, getX(), getY());
    }
}

private SimpleTimer timer = new SimpleTimer();
private Actor pursued;
private int bulletTimer;

public void act()
{
    if (!getObjectsInRange(650, Player_Test1.class).isEmpty())
    {
        if (pursued == null)
        {
            pursued = getObjectsInRange(650, Player_Test1.class).get(0);
        }
        if (!los.obstructedView(this, pursued, Walls.class))
        {
            pursue();
        }
        else
        {
            randomMovement();
        }
    }
    else
    {
        pursued = null;
        randomMovement();
    }
}