public function testGenerateRandStr()
 {
     $rand_array = array();
     for ($i = 0; $i < 10000; $i++) {
         $rand_array[] = OAuth2Util::generateRandStr();
         $this->assertNotNull($rand_array[$i]);
         $this->assertEquals(strlen($rand_array[$i]), 32);
     }
     $this->assertEquals($rand_array, array_unique($rand_array));
 }