function run_test() { var zReader = Components.classes["@mozilla.org/libjar/zip-reader;1"] .createInstance(Components.interfaces.nsIZipReader); try { zReader.open(null); do_throw("Shouldn't get here!"); } catch (e if (e instanceof Components.interfaces.nsIException && e.result == Components.results.NS_ERROR_NULL_POINTER)) { // do nothing, this test passes } }