PHPUnit Fatal error: requiere() when running

I'm new at PHPUnit and I'm having a problem when running the test. I noticed that the problem was that I was not including the class I supposed to test so I put the following line:

require '../../files/Cliente.php';

But then it gaves me the next error:

PHP Warning:  require(../../files/Cliente.php): failed to open stream: No such file or directory in /home/esperanza/Escritorio/clasificadosj-clasificados-7da0b31e6060/pruebas/files/ClienteTest.php on line 6

PHP Fatal error:  require(): Failed opening required '../../files/Cliente.php' (include_path='.:/usr/share/php:/usr/share/pear') in /home/esperanza/Escritorio/clasificadosj-clasificados-7da0b31e6060/pruebas/files/ClienteTest.php on line 6

My directory structure is the next:

Project
    |_files
      |_Cliente.php
    |_Test
      |_ClienteTest.php

I don't know if I have to configure a XML document or a bootstrap first.

Thanks a lot!