Object reference not set to an instance of an object

I am trying to reference a script but it keeps giving me this error. This is the code

 var AttackCombo : AttackCombo;
 function Awake ()
 {
 AttackCombo.Test();

and this is the script i'm trying to reference

 public var attackTime : float[]; // store each length of each attack in order (in the inspector)
 //public var attackAnimations : AnimationClip[]; // store a reference to the animations, then use the same index 'attackType'
  
 public var waitTime : float = 10; // how long player has to hit LMB after last attack has finished
  
 private var attackTimer : float = 0.0; // timer variable
 private var attackType : int = -1; // reference to what attack the combo is up to (-1 is none, 0+ is the array index for attackTime )
 //private var attack
  
 enum attack { Idle, Attacking, Waiting } // different states while the combo inputs are being checked
 var attackState : attack; // current attack input state (public for viewing in the Inspector)
 var test : int = 0;
  
 var totalChainedHits : int = 0; // total Chained Hits without missing a LMB press (public for viewing in the Inspector)
  
  
 function Start() 
 {
     // set defaults
     attackType = -1;
     attackState = attack.Idle;
     // tell animation to play Idle
     totalChainedHits = 0;
  
     // You could set up the attackTime array here (and make it private)
     
     attackTime = new float[3];
     attackTime[0] = 0.5;
     attackTime[1] = 0.5;
     attackTime[2] = 0.5;
     
 }
 
 function Test () {
     test++;
 }
  
 function Update() 
 {
     CheckForPlayerAttackInput();
 }
  
 function CheckForPlayerAttackInput() 
 {
     switch( attackState ) // what state is the combo in
     {
        case attack.Idle :
          if ( Input.GetMouseButtonDown(0) ) // start attacking
          {
              animation.CrossFade("Attack");
              attackType = 0;
              attackState = attack.Attacking;
              attackTimer = attackTime[0];
              // tell animation to play attack 0 (first attack)
              totalChainedHits = 1;
          }
        break;
  
        case attack.Attacking :
          attackTimer -= Time.deltaTime; // wait for attackTimer
  
          if ( attackTimer < 0 )
          {
              attackTimer = waitTime;
              attackState = attack.Waiting;
          }
  
          /* // uncomment this to break the combo while attacking
          if ( Input.GetMouseButtonDown(0) ) // break attack
          {
              attackType = -1;
              attackState = attack.Idle;
              // tell animation to play Idle
          }
          */
        break;
  
        case attack.Waiting :
          attackTimer -= Time.deltaTime; // check the Waiting Timer (attackTimer)
  
          if ( attackTimer < 0 ) // ran out of time to chain combo
          {
              attackType = -1;
              attackState = attack.Idle;
           //   animation.CrossFade("Idle");
              // tell animation to play Idle
          }
  
          if ( Input.GetMouseButtonDown(0) ) // continue attacking
          {
       //   animation.CrossFade("Attack1");
           attackType ++; // go to next attack
  
           if ( attackType >= attackTime.Length ) // check if the combo is over, start a new combo
           {
               attackType = 0;
               attackState = attack.Attacking;
               attackTimer = attackTime[0];
               // tell animation to play attack 0 (first attack)
                animation.CrossFade("Attack");
               totalChainedHits ++;
           }
           else
           {
               attackState = attack.Attacking;
               attackTimer = attackTime[ attackType ];
               animation.CrossFade("Combo");
               // tell animation to play attack 'attackType' (next attack in array)
               totalChainedHits ++;
           }
          }
        break;
     }
 }
  
 // example GUI for testing this script
 function OnGUI() 
 {
     GUI.Box( Rect( 10, 10, 100, 25 ), "Hit " + attackType.ToString() );
     GUI.Box( Rect( 10, 60, 100, 25 ), "Hit " + test.ToString() );
     GUI.Box( Rect( (Screen.width * 0.5) - 50, 10, 100, 25 ), "" + attackState.ToString() );
     GUI.Box( Rect( Screen.width - 110, 10, 100, 25 ), "Total " + totalChainedHits.ToString() );
     GUI.Box( Rect( (Screen.width * 0.5) - 50, 45, 100, 25 ), "" + attackTimer.ToString() );
 }