public void TakeDamage_Attacked_HealthEqual()
    {
        HealthLevel health = new HealthLevel();

        health.currentHealth = 5;

        health.TakeDamage(5);

        Assert.AreEqual(0, health.currentHealth);
    }
    //This method is used to check whether collision happen
    void OnTriggerEnter(Collider other)
    {
        //Generate explosion effect of asteroid when collision happen
        Instantiate(explosion, transform.position, transform.rotation);

        //If asteroid collide with player's ship
        if (other.tag == "Player")
        {
            //Generate explosion effect of player's ship
            Instantiate(explosion, other.transform.position, other.transform.rotation);
            Destroy(gameObject);

            GameObject playerObject = GameObject.FindWithTag("Player");
            if (playerObject != null)
            {
                healthLevel = playerObject.GetComponent <HealthLevel>();
            }

            if (playerObject == null)
            {
                Debug.Log("Cannot find 'HealthLevel' script");
            }

            //player's ship take damage of 5
            healthLevel.TakeDamage(5);
            healthLevel.UpdateHealth();

            //end the game and destroy player's ship when health is below 0
            if (healthLevel.currentHealth <= 0)
            {
                other.gameObject.GetComponent <PlayerController> ().alive = false;                //Buttons to show up, restart and mainmenu
                Destroy(other.gameObject);
                gameController.GameOver();
                Time.timeScale = 0;                 //The asteroids will stop spawning
            }
        }

        //If asteroid collide with player's bullets
        else
        {
            Destroy(other.gameObject);
            Destroy(gameObject);
        }

        gameController.AddScore(scoreValue);        //Adds score once object is hit
    }
    //This method is used to check whether collision happen
    void OnTriggerEnter(Collider other)
    {
        //Generate explosion effect of asteroid when collision happen
        Instantiate(explosion, transform.position, transform.rotation);

        //If asteroid collide with player's ship
        if (other.tag == "Player")
        {
            //Generate explosion effect of player's ship
            Instantiate(explosion, other.transform.position, other.transform.rotation);
            Destroy(gameObject);

            GameObject playerObject = GameObject.FindWithTag("Player");
            if (playerObject != null)
            {
                healthLevel = playerObject.GetComponent <HealthLevel>();
            }

            if (playerObject == null)
            {
                Debug.Log("Cannot find 'HealthLevel' script");
            }

            //player's ship take damage of 5
            healthLevel.TakeDamage(5);
            healthLevel.UpdateHealth();

            //end the game and destroy player's ship when health is below 0
            if (healthLevel.currentHealth <= 0)
            {
                Destroy(other.gameObject);
                gameController.GameOver();
            }
        }

        //If asteroid collide with player's bullets
        else
        {
            Destroy(other.gameObject);
            Destroy(gameObject);
        }
    }