="time_input" min="21:13" step="60" value="20:13">

<script>
    var input_number = document.getElementById("input_number");
    input_number.max = "30";
    input_number.step = "3";
    input_number.value = "30";
    input_number.stepDown(5);

    if (typeof(input_number.stepDown) == "function") {
      test(function() {
        assert_equals(input_number.value, "15", "call of stepDown method is failed.");
      });
    } else {
      test(function() {
        assert_unreached("stepDown attribute is not ex