ปัญหาในการใช้งาน Singleton Pattern

class Cfg
{
    /**
     * property ของคลาส
     *
     * @var int
     */
    public $property = 1;
   
    .........................

    /**
     * @param int $dec
     * @return int
     */
    public function inc($dec)
    {
        $this->property = $this->property + $dec;
        return $this->property;
    }
}

/**
 * Generated by PHPUnit_SkeletonGenerator on 2015-12-04 at 18:54:14.
 */
class CfgTest extends PHPUnit_Framework_TestCase
{
    /**
     * @var Cfg
     */
    protected $object;

    /**
     * Sets up the fixture, for example, opens a network connection.
     * This method is called before a test is executed.
     */
    protected function setUp()
    {
        $this->object = \Cfg::getInstance();
    }

    /**
     * Tears down the fixture, for example, closes a network connection.
     * This method is called after a test is executed.
     */
    protected function tearDown()
    {

    }

    /**
     * @covers Cfg::inc
     */
    public function testInc()
    {
        $this->assertEquals(2, $this->object->inc(1));
    }

    /**
     * @covers Cfg::inc
     */
    public function testInc2()
    {
        $this->assertEquals(2, $this->object->inc(1));
    }
}

class Cfg
{

    .........................


    public function reset()
    {
        $this->property = 1;
    }
}

class CfgTest extends PHPUnit_Framework_TestCase
{
    ......

    public function testInc()
    {
       $this->object->reset();
        $this->assertEquals(2, $this->object->inc(1));
    }

    public function testInc2()
    {
       $this->object->reset();
        $this->assertEquals(2, $this->object->inc(1));
    }
}

Cfg::getInstance()->inc(1);
Cfg::getInstance()->inc(1);
Cfg::getInstance()->inc(1);
Cfg::getInstance()->inc(1);
Cfg::getInstance()->inc(1);

$cfg = Cfg::getInstance();
$cfg->inc(1);
​$cfg->inc(1);
​$cfg->inc(1);
​$cfg->inc(1);
​$cfg->inc(1);