Test what happens when you set the window's prototype to various values. On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE". PASS __proto__ = window; __proto__ threw exception TypeError: Immutable prototype object '#' cannot have their prototype set. PASS __proto__ = chainPointingBackToWindow; __proto__ threw exception TypeError: Immutable prototype object '#' cannot have their prototype set. PASS __proto__ = 1; __proto__ is originalWindowPrototype PASS __proto__ = 'a string'; __proto__ is originalWindowPrototype PASS __proto__ = anotherObject; __proto__ threw exception TypeError: Immutable prototype object '#' cannot have their prototype set. PASS anotherObject.__proto__ = window; __proto__ is originalWindowPrototype PASS __proto__ = 1; __proto__ is originalWindowPrototype PASS __proto__ = 'a string'; __proto__ is originalWindowPrototype PASS __proto__ = anotherObject; __proto__ threw exception TypeError: Immutable prototype object '#' cannot have their prototype set. PASS __proto__ = originalWindowPrototype; __proto__ is originalWindowPrototype PASS anotherObject.__proto__ = window; anotherObject.__proto__ is window PASS __proto__ = null; __proto__ threw exception TypeError: Immutable prototype object '#' cannot have their prototype set. PASS location.__proto__.__proto__ = location threw exception TypeError: Immutable prototype object '#' cannot have their prototype set. PASS successfullyParsed is true TEST COMPLETE