When you go to the Simulation page, there are three options: Learn Mode, Practice Mode, and Test Mode.
Click on Start Test to launch a Test Mode scenario. Note that the system will choose a scenario at random for you - you can't choose a specific one in Test Mode. As long as you have previously done all the scenarios in Learn Mode and Practice Mode you will be fine!
By the way, if the Test Mode box on that page is greyed out so you can't click on Start Test, this means you have another simulation scenario selection open for either Learn Mode or Practice Mode. Close that scenario selection window by clicking on the X in the top right corner of the small window.
Hopefully this answers your question, but feel free to message our support team if you need additional assistance.