Here is the Apex Class

public class AssignLeadsUsingAssignmentRules
{
    @InvocableMethod
    public static void LeadAssign(List<Id> LeadIds)
    {
            Database.DMLOptions dmo = new Database.DMLOptions();
            dmo.assignmentRuleHeader.useDefaultRule= true;          
            Lead Leads=[select id,OwnerId from lead where lead.id in :LeadIds];
            Leads.setOptions(dmo);
        	system.debug('Before Update Lead Details' + Leads);
         	Database.update(Leads,dmo);
        	Lead Leads2=[select id,OwnerId from lead where lead.id in :LeadIds];
        	system.debug('After Update Lead Details' + Leads2);
   }
}

Here is the test class 

@isTest 
      public class TestAssignLeadsUsingAssignmentRules{
      static testMethod void createnewlead() {
     
   //   Test.startTest();    
      Lead leadToCreate =new Lead();
      List<id> Ids= New List<Id>();
    //  leadToCreate.ownerid= userToCreate.id;
      leadToCreate.ownerid= UserInfo.getUserId();  
      leadToCreate.LastName ='Sample1';
      leadToCreate.Email='Someone@somewhere.com';
      leadToCreate.Company='OneTwo34';
      leadToCreate.LeadSource='Partner Referral';
      leadToCreate.Country='IN';
      leadToCreate.Source_Last_Lead_Source_Detail__c='Form - Contact Form';
          
      insert leadToCreate; 
      
      Ids.add(leadToCreate.id);
      AssignLeadsUsingAssignmentRules.leadAssign(Ids);
      System.assertEquals('00G1W000002RyhMUAS', leadToCreate.OwnerId, 'Something is wrong');

 	//  Test.stopTest();
      
   }
}

The test class fails as shown below As you can see the debug log shows the lead OwnerId has changed but the change does not persist outside the class in the test. What am I missing? 

Here is the Apex Class

public class AssignLeadsUsingAssignmentRules
{
    @InvocableMethod
    public static void LeadAssign(List<Id> LeadIds)
    {
            Database.DMLOptions dmo = new Database.DMLOptions();
            dmo.assignmentRuleHeader.useDefaultRule= true;          
            Lead Leads=[select id,OwnerId from lead where lead.id in :LeadIds];
            Leads.setOptions(dmo);
        	system.debug('Before Update Lead Details' + Leads);
         	Database.update(Leads,dmo);
        	Lead Leads2=[select id,OwnerId from lead where lead.id in :LeadIds];
        	system.debug('After Update Lead Details' + Leads2);
   }
}

Here is the test class 

@isTest 
      public class TestAssignLeadsUsingAssignmentRules{
      static testMethod void createnewlead() {
     
   //   Test.startTest();    
      Lead leadToCreate =new Lead();
      List<id> Ids= New List<Id>();
    //  leadToCreate.ownerid= userToCreate.id;
      leadToCreate.ownerid= UserInfo.getUserId();  
      leadToCreate.LastName ='Sample1';
      leadToCreate.Email='Someone@somewhere.com';
      leadToCreate.Company='OneTwo34';
      leadToCreate.LeadSource='Partner Referral';
      leadToCreate.Country='IN';
      leadToCreate.Source_Last_Lead_Source_Detail__c='Form - Contact Form';
          
      insert leadToCreate; 
      
      Ids.add(leadToCreate.id);
      AssignLeadsUsingAssignmentRules.leadAssign(Ids);
      System.assertEquals('00G1W000002RyhMUAS', leadToCreate.OwnerId, 'Something is wrong');

 	//  Test.stopTest();
      
   }
}

The test class fails as shown below As you can see the debug log shows the lead OwnerId has changed but the change does not persist outside the class in the test. What am I missing?