code: func Set(c context.Context, mr *rand.Rand) context.Context {
  	var r Rand
  	if mr != nil {
  		r = wrapRand(mr)
  	}
  	return SetRand(c, r)
  }
docs: // Set sets the current *"math/rand".Rand object in the context.
  //
  // Useful for testing with a quick mock. The supplied *rand.Rand will be wrapped
  // in a *Locking if necessary such that when it is returned from Get, it is
  // safe for concurrent use.