I am using PHPStorm to run unit tests using PHPUnit, some previous tests have worked but now all tests are failing with exit code 255

I am using PHPStorm to run unit tests using PHPUnit, some previous tests have worked but now all tests are failing with exit code 255.

Some previous tests have worked but now all tests seem to fail. I haven't changed any configuration settings, all I have done is created a new test.

I have read on so many things but nothing seems to work and really need help.

here are my configuration settings:

config settings

And here is a test that has recently passed but now fails.

use app\Mailer;
require_once '../app/Mailer.php';

class MailerTest extends \PHPUnit_Framework_TestCase

 private $_mailer;

public function setUp()
{
    $this->_mailer = new Mailer();

}

public function tearDown(){}

public function testMailerClass()
{
    $this->_mailer->Subject = "test email";
    $this->_mailer->Recipient = "email address";
    $this->_mailer->Message = "This is a test email";

    $this->assertTrue($this->_mailer->Send(), 'Expects an email to be sent');
}

}