Use Jetpack?  Occasionally write unit tests so you won’t be a complete hypocrite when criticizing other people’s code?  Think that picture up above looks more useful than this?:

error: fail: list contents ("4,5,6,7" != "3,4,5,6,7")
info: Traceback (most recent call last):
  File "resource://wmsy-jetpack-core-lib/timer.js", line 57, in notify
    this._callback.apply(null, []);
  File "resource://wmsy-jetpack-core-lib/unit-test.js", line 257, in anonymous
    timer.setTimeout(function() { onDone(self); }, 0);
  File "resource://wmsy-jetpack-core-lib/unit-test.js", line 282, in runNextTest
    self.start({test: test, onDone: runNextTest});
  File "resource://wmsy-jetpack-core-lib/unit-test.js", line 300, in start
    this.test.testFunction(this);
  File "resource://wmsy-jetpack-core-lib/unit-test.js", line 57, in runTest
    test(runner);
  File "resource://wmsy-wmsy-tests/test-vs-static.js", line 37, in anonymous
    slice.seek(6, 2, 2);
  File "resource://wmsy-wmsy-lib/wmsy/viewslice-static.js", line 51, in anonymous
    this._list.slice(this.bufLow, this.bufHigh));
  File "resource://wmsy-wmsy-tests/test-vs-static.js", line 31, in anonymous
    "list contents");
  File "resource://wmsy-jetpack-core-lib/unit-test.js", line 229, in assertEqual
    this.fail(message);
  File "resource://wmsy-jetpack-core-lib/unit-test.js", line 147, in fail
    console.trace();

Then do I have an .el for you!  This lives here.  You mileage may vary and may involve things catching on fire which can, in turn, affect your mileage.