In my dog dildo guide, I go over the top 20 canine dildos.  These are very anatomically correct and have a large bulbus glands ‘knot’ towards the base of the dildo.  
These knots are not testicles.  When an actual wolf has sex this ‘bulb’ or knot fills up with blood once the penis is inserted inside the female.  After it is fully engorged it works as a tie that keeps the wolf’s penis from falling out.