PHPUnit object initialized in setUp() becomes null after 1st test

I am new to PHPunit and while learning it with sample classes, I am getting error. The error is that, the Object $this->sysman, that is initialized in setUp() becomes null after execution of the 1st test. Below is code, which I am trying. Please let me know what is mistake here. Thanks.

class PersonTest extends TestCase {

/** @var SysManService $sysman */
protected $sysman;
protected $personModel;

public function setUp(){
    /** @var Adapter $adapter */
    $adapter = $this->prophesize(Adapter::class)->reveal();

    /** @var LoggerService $logger */
    $logger = $this->prophesize(LoggerService::class)->reveal();

    /** @var  ContainerInterface $container */
    $container = $this->prophesize(ContainerInterface::class);
    $config = (array)$container->get('config');

    $this->sysman = new SysManService($adapter, $logger, $config);
    //$sysman = new SysManService($adapter, $logger, $config);

    $this->personModel = new Person($this->sysman);
  }

protected function tearDown(){ }

public function testPropertyUserNameExists() {
    $this->assertObjectHasAttribute('userName', $this->personModel);
}

public function testPropertyPasswordExists() {
    $this->assertObjectHasAttribute('password', $this->personModel);
}}