Testis pain = see Dr
usually means a trip to the doctor because the testicle's blood supply can be twisted off (called torsion).
When that happens, the testicle can die. Other causes of testicle pain include trauma, infection, twisting off an appendix of a testicle (a small lump next to a testicle), etc... Since a guy usually cannot tell if his testicle is twisted, an exam by the doctor is needed.