[SalesForce] Test Class Coverage Issue with Trigger.newMap != Trigger.oldMap

I'm hoping I am missing something obvious.

I have a Lead Trigger & Handler class. The Handler forces Assignment Rules to fire if a Lead Checkbox field IS CHANGED to True. After Update. It is working for users.

The problem is my Handler test class coverage stops right at the line where I am checking whether the field "Attention Required" has been changed to true:

  public class LeadTriggerHandler extends TriggerHandlerFactory{
  private Map<Id, Lead> newLeadMap;
  private Map<Id, Lead> oldLeadMap;

  public LeadTriggerHandler() {
    this.newLeadMap = (Map<Id, Lead>) Trigger.newMap;
    this.oldLeadMap = (Map<Id, Lead>) Trigger.oldMap;
  }

    public override void afterUpdate() {
        try{
        attentionRequiredLeadAssignment();
        }catch(Exception e){
            Utils.CreateSystemException(e);
        }
    }   

  /*
  * If a Lead is set to "Attention Required"
  * and is owned by one of the following Queues: Recycle, Nurture, Junk
  * then trigger Assignment Rules to reassign Lead
  */
  private void attentionRequiredLeadAssignment() {
    List<Lead> leads = new List<Lead>();
    List<String> queueNameList = new List<String>();
    Set<String> queueNameSet = new Set<String>();

    for(Lead l : [SELECT Id,attention_required__c,Owner.Name FROM Lead WHERE Id IN :newLeadMap.keyset()]){
      //if attention required is changed to TRUE
      if(newLeadMap.get(l.id).attention_required__c != oldLeadMap.get(l.id).attention_required__c && newLeadMap.get(l.id).attention_required__c == true){
        //getting Queue names from custom setting
        LeadTriggerHandlerSetting__c setting = LeadTriggerHandlerSetting__c.getValues('AttentionRequired');
        queueNameList = setting.queue_names__c.split(','); 
        queueNameSet.addAll(queueNameList);
        //and lead owner is recycle, nurture, or junk leads
        if(queueNameSet.contains(l.Owner.Name)){
          leads.add(l);
        }
      }
    }

    if(!leads.isEmpty()) {
       Database.DMLOptions dmo = new Database.DMLOptions();
       //force assignment rules to fire
       dmo.assignmentRuleHeader.useDefaultRule = true;
       Database.SaveResult[] lsr = Database.update(leads, dmo);

       Integer i=0;
       for(Database.SaveResult sr : lsr) {
          if(!sr.isSuccess()){
              leads[i].addError('Lead Assignment Error' + sr.getErrors()[0].getMessage());
          }
          i++;
       } 
    }
  }


}

It seems obvious enough that in the Test Class I need to insert a Lead with "Attention Required" set to false, and then update it to true. However this is not getting me coverage past the line:

if(newLeadMap.get(l.id).attention_required__c != oldLeadMap.get(l.id).attention_required__c && newLeadMap.get(l.id).attention_required__c == true){

This is the Test Class:

@isTest
private class LeadTriggerHandlerTest
{
    @isTest
    static void testLeadAssignment() {
        Group testGroup = new Group(Name='Junk Leads', Type='Queue');
        insert testGroup;

        System.runAs(new User(Id=UserInfo.getUserId()))
        {
            QueuesObject testQueue = new QueueSObject(QueueID = testGroup.id, SObjectType = 'Lead');
            insert testQueue;
        }

        LeadTriggerHandlerSetting__c setting = new LeadTriggerHandlerSetting__c();
        setting.Name = 'AttentionRequired';
        setting.Queue_Names__c = 'Junk Leads,Nurture Pool';
        insert setting;

        DataFactory factory = new DataFactory();

        Lead l = factory.createLead();
        l.OwnerId = testGroup.id;
        l.Attention_Required__c = false;
        upsert l;

        l.Attention_Required__c = true;
        update l;
    }
}

Any ideas?