add annotation

Author: vladak

opengrok-indexer/src/main/java/org/opengrok/indexer/history/Annotation.java

@@ -24,6 +24,7 @@
  */
 package org.opengrok.indexer.history;
 
+import org.jetbrains.annotations.VisibleForTesting;
 import org.opengrok.indexer.logger.LoggerFactory;
 import org.opengrok.indexer.util.Color;
 import org.opengrok.indexer.util.LazilyInstantiate;
@@ -91,6 +92,7 @@ public Set<String> getRevisions() {
         return ret;
     }
 
+    @VisibleForTesting
     Set<String> getAuthors() {
         Set<String> ret = new HashSet<>();
         for (Line ln : this.lines) {