i have written a class,but both users are executing the class,but only user2 should insert the record what mistake is there in my class can annyone tell me.

class
public class inserting {
    public  void insertingrecords(string nm,decimal dd){
        Account a = new Account();
        a.name=nm;
        insert a;
    }
   
}

testclass using system.runas():
@isTest
private class TestRunAs {
   public static testMethod void testRunAs() {
      // Setup test data
      // This code runs as the system user
      Profile p = [SELECT Id,name FROM Profile WHERE Name='System Administrator']; 
               system.debug('values in p==='+'p.Name is '+p.name+'p.id is '+p.Id);
       
      /*User u = new User(Alias ='rprac', Email='sharath.kanukuntla1@gmail.com', 
      EmailEncodingKey='UTF-8', LastName='practise1', LanguageLocaleKey='en_US', 
      LocaleSidKey='en_US', ProfileId = p.Id, 
      TimeZoneSidKey='America/Los_Angeles', UserName='randheer.practise1@gmail.com');
      system.debug('user details are====== '+'email is '+u.Email+'Alias is '+u.Alias+'Profile id is '+u.ProfileId);
      
       System.runAs(u) {
         // The following code runs as user 'u' 
         System.debug('Current User: ' + UserInfo.getUserName());
         System.debug('Current Profile: ' + UserInfo.getProfileId()); 
      }*/
       User u3 = [SELECT Id FROM User WHERE UserName='randheer.practise1@gmail.com'];
         System.runAs(u3) {
             inserting obj = new inserting();
             obj.insertingrecords('sresht',12.22);
             System.debug('Current User: ' + UserInfo.getUserName());
             System.debug('Current Profile: ' + UserInfo.getProfileId()); 
             
         }
   }
}