1. Вариант;

  <?php namespace ClassTester;

 use PHPUnit_Framework_TestCase;
 use dataUser;
 use modelDBHandler;  // Указал !!!

 class ClassTester extends PHPUnit_Framework_TestCase {

 public function testExist(){
   $handler = new DBHandler();
   $exist = $handler->exist(new User(******", "*****", "*****", "*******"));
   if($exist){
       echo "User exist in database! ";
   }elseif(!$exist){
       echo "<pre>";
       echo "You need to register this user it is not exist! ";
       echo "</pre>";
   }
 }





2. Вариант;

      <?php

       use dataUser;

       class ClassTester extends PHPUnit_Framework_TestCase {

       public function testExist(){
       $handler = newmodelDBHandler();
       $exist = $handler->exist(new User(******", "*****", "*****", "*******"));
       if($exist){
           echo "User exist in database! ";
       }elseif(!$exist){
           echo "<pre>";
           echo "You need to register this user it is not exist! ";
           echo "</pre>";
       }
     }