Frankly speaking, giving just one or two SAP Fiori System Admin Certification practice test is not enough. You need to prepare continuously at least for a month to be sure that you will excel in the actual SAP C_FIORADM_21 certification exam.
There this site comes very handy. Once you enroll for it after giving the demo test, it gives you unlimited access to all the mock tests for 2 months. I have practiced for more than 1.5 months and cleared the exam with 90%.