IMO you can select the first test in proximity to your current status level (stars to diamonds count) but can continue up the ladder as you feel up to a challenge.
As your TL increases and fitness improves the higher up that ladder you can go.
For example, start at Level 02 (two diamonds) when at one to two star status then try 03, 04, etc, and see how far you get above your current status level before you admit defeat. 
A hardness test doesn’t have to be a prescribed workout but is best tackled after an easy or rest day.
@Cyclopaat – Kudos for reaching that level but sometimes I think you need to add a disclaimer to your posts. 
Your experience/advice reflects the upper end of the bell curve. I’ll bet the majority of Xert users don’t have the luxury to ride full time and many of us aren’t going to reach 4-5 star status even if we could ride 20 hours/week. 