Ideally, you would find a good AME schedule a non-FAA work-up/consultation and go over your options. You need to know what paperwork will need to be submitted to the FAA so you can have it ready to go at the time of your actual FAA Medical Exam. Generally, you would be unable to fly solo (this includes Sport Pilot) once you take an FAA medical and fail/get deferred. On an FAA medical exam there is only Pass, or Fail. Failure gets deferred to the FAA Aeromedical Division in Oklahoma City.
The Medical Flight Test (MFT) does not need to be part of a check ride for a certificate or rating, though it can be if you choose to and are qualified for the certificate or rating for which you are applying.
Bear in mind that getting approval from the FAA Aeromedical folks for a MFT can take 4-8 weeks and then getting scheduled with your Local FSDO can take 2 to 8 weeks. If your submitted paperwork is incomplete then you have to submit the missing or incomplete items and wait another 4-8 weeks.
If you know you will fail the vision test don't just barely fail it. Your Statement of Demonstrated Ability (SODA) will be based on the vision deficiency submitted by your AME. Thus if you can only see 20/25 make sure you test 20/40 in case your eyes get worse in the future. ALso a SODA is good for the class issued and below. a second class SODA can not be used for a First class Medical.
There are a lot of pilots out there with First and Second class medicals that have vision less than 20/20 so it can be done. Find an AME that wants to work with you.