public function test_custom_message()
 {
     BookNumericality::$validates_numericality_of = array(array('numeric_test', 'message' => 'Hello'));
     $book = new BookNumericality(array('numeric_test' => 'NaN'));
     $book->is_valid();
     $this->assert_equals(array('Numeric test Hello'), $book->errors->full_messages());
 }