01-test.js

// Taken from http://dxr.mozilla.org/mozilla-central/source/js/xpconnect/tests/chrome/test_xrayToJS.xul

    ...

    // Test constructors that can be instantiated with zero arguments.
    for (var c of simpleConstructors) {
      ok(iwin[c], "Constructors appear: " + c);
      is(iwin[c], Cu.unwaiveXrays(iwin.wrappedJSObject[c]),
         "we end up with the appropriate constructor: " + c);
      is(Cu.unwaiveXrays(Cu.waiveXrays(new iwin[c]).constructor), iwin[c],
         "constructor property is set up right: " + c);
      let expectedProto = /Opaque/.test(new iwin[c]) ? iwin['Object'].prototype
                                                     : iwin[c].prototype;
      is(Object.getPrototypeOf(new iwin[c]), expectedProto,
         "prototype is correct: " + c);
      is(global(new iwin[c]), iwin, "Got the right global: " + c);
    }

    // Test Object in more detail.
    var num = new iwin.Object(4);
    is(Cu.waiveXrays(num).valueOf(), 4, "primitive object construction works");
    is(global(num), iwin, "correct global for num");
    var obj = new iwin.Object();
    obj.foo = 2;
    var withProto = Cu.unwaiveXrays(Cu.waiveXrays(iwin).Object.create(obj));
    is(global(withProto), iwin, "correct global for withProto");
    is(Cu.waiveXrays(withProto).foo, 2, "Inherits properly");

    ...

02-test.js

// Clearly that could be rewritten like this:

  test("constructors that can be instantiated with zero arguments", function () {
    for (var c of simpleConstructors) {
      ok(iwin[c], "Constructors appear: " + c);
      is(iwin[c], Cu.unwaiveXrays(iwin.wrappedJSObject[c]),
         "we end up with the appropriate constructor: " + c);
      is(Cu.unwaiveXrays(Cu.waiveXrays(new iwin[c]).constructor), iwin[c],
         "constructor property is set up right: " + c);
      let expectedProto = /Opaque/.test(new iwin[c]) ? iwin['Object'].prototype
                                                     : iwin[c].prototype;
      is(Object.getPrototypeOf(new iwin[c]), expectedProto,
         "prototype is correct: " + c);
      is(global(new iwin[c]), iwin, "Got the right global: " + c);
    }
  });

  test("Object in more detail", function () {
    var num = new iwin.Object(4);
    is(Cu.waiveXrays(num).valueOf(), 4, "primitive object construction works");
    is(global(num), iwin, "correct global for num");
    var obj = new iwin.Object();
    obj.foo = 2;
    var withProto = Cu.unwaiveXrays(Cu.waiveXrays(iwin).Object.create(obj));
    is(global(withProto), iwin, "correct global for withProto");
    is(Cu.waiveXrays(withProto).foo, 2, "Inherits properly");

    ...
  });

// but then it is not clear what the code does. you must go find the test() function and read it to find out if the tests are run synchronously, conditionally, etc. so it's not zero cost is what i'm saying.