/**
  * testAt
  *
  * @return  void
  */
 public function testAt()
 {
     $string = 'Foo Bar';
     $this->assertEquals('F', StringHelper::at($string, 0));
     $this->assertEquals('o', StringHelper::at($string, 1));
     $this->assertNull(StringHelper::at($string, 10));
 }