gecko-dev/xpcom/tests/unit/test_bug325418.js

// 5 seconds.
const kExpectedDelay1 = 5;
// 1 second.
const kExpectedDelay2 = 1;

var gStartTime1;
var gStartTime2;
var timer;

var observer1 = {
  observe: function observeTC1(subject, topic, data) {
    if (topic == "timer-callback") {
      // Stop timer, so it doesn't repeat (if test runs slowly).
      timer.cancel();

      // Actual delay may not be exact, so convert to seconds and round.
      Assert.equal(
        Math.round((Date.now() - gStartTime1) / 1000),
        kExpectedDelay1
      );

      timer = null;

      info(
        "1st timer triggered (before being cancelled). Should not have happened!"
      );
      Assert.ok(false);
    }
  },
};

var observer2 = {
  observe: function observeTC2(subject, topic, data) {
    if (topic == "timer-callback") {
      // Stop timer, so it doesn't repeat (if test runs slowly).
      timer.cancel();

      // Actual delay may not be exact, so convert to seconds and round.
      Assert.equal(
        Math.round((Date.now() - gStartTime2) / 1000),
        kExpectedDelay2
      );

      timer = null;

      do_test_finished();
    }
  },
};

function run_test() {
  do_test_pending();

  timer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);

  // Initialize the timer (with some delay), then cancel it.
  gStartTime1 = Date.now();
  timer.init(
    observer1,
    kExpectedDelay1 * 1000,
    timer.TYPE_REPEATING_PRECISE_CAN_SKIP
  );
  timer.cancel();

  // Re-initialize the timer (with a different delay).
  gStartTime2 = Date.now();
  timer.init(
    observer2,
    kExpectedDelay2 * 1000,
    timer.TYPE_REPEATING_PRECISE_CAN_SKIP
  );
}