func NewSubscriber(activityChan <-chan *vocab.ActivityType) *Subscriber {
	s := &Subscriber{
		activityChan: activityChan,
	}
	go s.listen()
	return s
}
NewSubscriber returns a new mock activity subscriber.
package mocks
import (
	"sync"
	"github.com/trustbloc/orb/pkg/activitypub/vocab"
)
type Subscriber struct {
	activityChan <-chan *vocab.ActivityType
	mutex        sync.Mutex
	activities   []*vocab.ActivityType
}