Fatal error: class not found in php unit test

I am trying to run phpunit manually as following from the command line in the proper directory:

phpunit UtilitiesTest UtilitiesTest.php

Yet, I get the following error message:

Fatal error: Class 'Testdir1dir2Utilities' not found in
/Test/dir1/dir2/UtilitiesTest.php on line 35
Class 'Testdir1dir2Utilities' not found

Line 35 is:

$retr = Utilities::toMySqlSQLStringDate($toTest);

At the begiing of UtilitiesTest.php, I have:

namespace Testdir1dir2;

use PHPUnit_Framework_TestCase;
use some_pathdir1dir2Utilities;

Yet, the file is available in a file called Utilities.class.php in Tfrdir1dir2.

Does anyone know what is happening?