gecko-dev/netwerk/test/unit/test_gre_resources.js

// test that things that are expected to be in gre-resources are still there
Cu.import("resource://gre/modules/NetUtil.jsm");

var ios = Cc["@mozilla.org/network/io-service;1"]. getService(Ci.nsIIOService);

function wrapInputStream(input)
{
  var nsIScriptableInputStream = Components.interfaces.nsIScriptableInputStream;
  var factory = Components.classes["@mozilla.org/scriptableinputstream;1"];
  var wrapper = factory.createInstance(nsIScriptableInputStream);
  wrapper.init(input);
  return wrapper;
}

function check_file(file) {
  var channel = NetUtil.newChannel({
    uri: "resource://gre-resources/"+file,
    loadUsingSystemPrincipal: true
  });
  try {
    let instr = wrapInputStream(channel.open2());
    do_check_true(instr.read(1024).length > 0)
  } catch (e) {
    do_throw("Failed to read " + file + " from gre-resources:"+e)
  }
}

function run_test() {
  for (let file of ["ua.css"])
    check_file(file)
}