trigger Prefix_Dr on Lead (before insert,before update) {
    for(lead L:trigger.new){
       L.FirstName='Dr.'+L.FirstName;
        }
}
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
@istest
public class Prefix_Dr_test {
    testmethod static void test(){
        Lead L=New Lead();
        L.FirstName='Dr.Midul';
        L.LastName='ahmed';
        L.Company='sfdc';
        L.Status='Working-contacted'; 
        insert L;
        
        Lead Le=[select Id,firstname,lastname from lead where company='sfdc'];
       System.assertEquals(Le.FirstName.ContainsIgnoreCase('Dr.'),'Dr.');
           
    }


here test class is showing error