Hi ,
I'm very new to triggers and managed to write a trigger and it works in Sandbox  and it's test cass is success but not covering code coverage show only 0. Unable to achieve code coverage, any suggestions to direct me to achieve my 100% code coverage.

I appreciate you help in advance!!

My trigger:

trigger parentCaseClose on case(before update)
{
    set<id> openCaseIDs = new set<id>();
    
    for(case caseList : [select id, ParentId, status from case where ParentId In:trigger.newMap.keyset() AND status != 'Closed'])
    {
        openCaseIDs.add(caseList.ParentId);
    }
    
    for(case newCase : trigger.new)
    {
        if(newCase.status != trigger.oldMap.get(newCase.id).status && newCase.status == 'Closed' && openCaseIDs.contains(newCase.id))
        {
            newCase.addError('The associated child cases are open');
        }
    }
}



My Test class:

@isTest

private class TestParentCaseCloseValidation {
   
  public static List<Case> createCase(string caseStatus) {
     // test account insert
    Account a = new Account();
       a.Name = 'sample account';
       insert a;
    // test contact insert
     Contact c = new Contact();
        c.FirstName = 'Test';
        c.LastName = 'contact';
        c.AccountId= a.Id;
        insert c;
        
     List<Case> cases = new List<Case>();
    // string caseStatus = 'In Progress';
     Case parent = new Case( Subject='TEST', contactID = c.id,Status=caseStatus );
        insert parent;
       
     cases.add(parent);
       // system.debug('insert parent',cases.isEmpty());
    
     Case child1 = new Case(Subject='child1',  contactID = c.id, Status=caseStatus,ParentId=parent.Id);
        insert child1;
        cases.add(child1);
    
    
     Case child2 = new Case(Subject='child2', contactID = c.id, Status=caseStatus,ParentId=parent.Id);
        insert child2;
        cases.add(child2);
        return cases;
    
    
    
 }
   
     static testMethod void testCloseParent() {
      
        List<Case> cases = createCase('In Progress');
            String parentId = null;
     //Update one of the children and see that the parent stays open
          for (Case c:cases) {
              if (c.ParentId!=null) {
                  parentId = c.ParentId;
                  c.Status = 'Closed';
                 
                }
          }
        update cases;
        //Shouldn't be closed yet
            Case parent = [select IsClosed from Case where Id=:parentId];
                System.assert(parent.IsClosed==false);
               
             for (Case c:cases) {
                    if (c.ParentId!=null && c.Status!='Closed') {
                        parentId = c.ParentId;
                        c.Status = 'Closed';
                       
                      
                    }
                }update cases;
        
       
    
       
        test.startTest();
                          
    try
   
        {
            update parent;
 
        }

        catch(System.DMLException e)

        {

            System.assert(e.getMessage().contains('There are still Child Cases Open '));

        }
     test.stopTest();
    }
}