on step value 24 hour");
test(function(){
  _StepTest.value = "23:59:59";
  _StepTest.step = "86399";
  _StepTest.stepDown();
  assert_in_array(
    _StepTest.value,
    [
      "00:00",
      "00:00:00",
      "00:00:00.0",
      "00:00:00.00",
      "00:00:00.000"],
    "a valid time string representing midnight");
} , "stepDown on step value 24 hour ");

test(function(){
  _StepTest.value = "12:00";
  _StepTest.step = "3600";
  _StepTest.stepUp();
  assert_in_array(
    _StepTest.value,
    [
      "13:0