Concept: Add a test mode to exercises

Have you ever felt depressed after answering a question wrong? With test mode, that depress will go away (at least until you submit the work). Test mode is designed to help you do exercises as actual tests, navigating between questions at will, managing your time, and reviewing.

Idea:

- Before starting an exercise, there will be a check box called "Test mode" with its brief description below. If you turn it on, you can also set the timer for the test. It have some options such as disabled, 5 minutes, 10 minutes, 20 minutes, or a custom time.

- The questions are still normal, except now it's a test, and you can only know the answer after submitting. Before the timer runs out, you can switch between questions, mark a question for reviewing, and do anything just like in online tests.

- If you use a hint, that question will be marked "Hinted"

If you want this feature to be added in the official website, please leave a vote.