Add tests for cache and locking

Signed-off-by: Gabriel Adrian Samfira <gsamfira@cloudbasesolutions.com>

locking/interface.go

@@ -5,6 +5,7 @@ import "time"
 type Locker interface {
 	TryLock(key, identifier string) bool
 	Lock(key, identifier string)
+	LockedBy(key string) (string, bool)
 	Unlock(key string, remove bool)
 	Delete(key string)
 }