/**
  * @param string $identifier
  * @return boolean
  */
 public function exists($identifier)
 {
     return $identifier === 'incrementer' || $identifier === 'random' || parent::exists($identifier);
 }
 /**
  * @test
  */
 public function testSleepReturnsExpectedPropertyNames()
 {
     $subject = new StandardVariableProvider();
     $properties = $subject->__sleep();
     $this->assertContains('variables', $properties);
 }