From your letter,i came to know that you are feeling a ball like swelling above left testis.It is not an Extra testicle.
Most probably,it could be a Cystic swelling arising from Epididymis
, a structure which is attached to testis and just above it or Spermatocele
But,you should consult Urologist/General surgeon
and get it examined.
Simple test like Ultrasound
of the scrotum may clinch the diagnosis.
wish you good health