There is a test.
class CMethodTest extends CTestCase{
    public $a = 1;
    public static function setUpBeforeClass(){
        $a='Before';
    }
    public function testZ(){
        $this->a = 'z';
    }
    public function testAb(){
        $this->a = 'b';
    }
    public function testE(){
        var_dump($this->a);
    }
}
The test has 3 methods. Inside these methods $this->a is trying to change. As a result $this->a equal "1".
Why Can not i change $this->a?