There is no use for testosterone in semen. What would you think testosterone would be need in semen to do?  

Semen contains chemicals which get the sperm to the egg.  That is what the whole idea is about.  This having fun thing is really part of the same goal.  There is some slippery slidy stuff, some keep it moist stuff, and some stuff to help penetrate the egg surface.  You need the testosterone to tell you it's time to go for it, don't want to make it in a place where it's won'd do any good.

The composition of semen will amaze you. it contains very modest quantities of the following substances: aboutonia, ascorbic acid, blood-group antigens, calcium, chlorine, cholesterol, choline, citric acid, creatine, deoxyribonucleic acid, fructose, glutathione, hyaluronidase, inositol, lactic acid, magnesium, nitrogen, phosphorus, potassium, purine, pyrimidine, pyruvic acid, sodium, sorbitol, spermidine, spermine, urea, uric acid, vitamin B12, and zinc.

hormones, like testosterone, are substances secreted into the bloodstream which travel to the brain and cause things to happen in the body - like hair growth, sperm production, etc. testosterone goes from the testes to the bloodstream to the brain.... it is not excreted in ejaculate.

does that explain it?