It appears that this test doesn't cause the trigger to fire.  Please help.

Trigger

trigger CaptureLevel1Owner on Case (before update) {
           
      for(Case c: Trigger.new) {
        String caseLevel2 = 'Level 2';
        if (Trigger.isUpdate) {
          if (c.Level__c == caseLevel2) {        
                   if (c.Level_1_Owner__c == null)
              c.Level_1_Owner__c = c.Level_1_Case_Owner_Id__c;
           }
         }
      }
 }

Test Class

@isTest
 private class TestCaptureLevel1Owner {
   static testMethod void testLevelTrigger() {
     Case[] myCase = new Case[] { 
         new Case(Subject = 'Trigger Test', Status = '10-Working',
         Level__c = 'Level 1', Level_1_Owner__c = null,
         OwnerId = '00580000001Usii', Level_1_Case_Owner_Id__c = '00580000001Usii' ) } ; 
    insert myCase;
    System.assert(myCase[0].Level_1_Owner__c == null);
    System.assert(myCase[0].Level__c == 'Level 1');
    System.assert(myCase[0].OwnerId == '00580000001Usii');
     
     myCase[0].Level__c = 'Level 2';
    
//   Verify that conditions are set so that trigger will fire    
     System.assert(myCase[0].Level_1_Owner__c == null);
     System.assert(myCase[0].Level__c == 'Level 2');
    
//   and that the Level 1 Owner ID is not empty so there is something for the trigger to load
     System.assert(myCase[0].Level_1_Case_Owner_Id__c != null);
   
     update myCase;
     
//   This should fail since the trigger should have loaded Level 1 Owner,
//   but it doesn't which implies that the trigger isn't firing     
     System.assert(myCase[0].Level_1_Owner__c == null);
           
     
//     System.assertEquals(c.Level_1_Owner__c,c.Level_1_Case_Owner_Id__c);
 
 //    System.assert(c.Level_1_Owner__c == c.Level_1_Case_Owner_Id__c);
     

   }     
 }