HDFS-13159. TestTruncateQuotaUpdate fails in trunk. Contributed by Nanda kumar.

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestTruncateQuotaUpdate.java

@@ -22,6 +22,8 @@ import org.apache.hadoop.fs.permission.PermissionStatus;
 import org.apache.hadoop.hdfs.protocol.Block;
 import org.apache.hadoop.hdfs.server.blockmanagement.BlockInfo;
 import org.apache.hadoop.hdfs.server.blockmanagement.BlockInfoContiguous;
+import org.apache.hadoop.hdfs.server.namenode.snapshot.DiffList;
+import org.apache.hadoop.hdfs.server.namenode.snapshot.DiffListByArrayList;
 import org.apache.hadoop.hdfs.server.namenode.snapshot.FileDiff;
 import org.apache.hadoop.hdfs.server.namenode.snapshot.FileDiffList;
 import org.apache.hadoop.hdfs.server.namenode.snapshot.FileWithSnapshotFeature;
@@ -156,11 +158,11 @@ public class TestTruncateQuotaUpdate {
     FileDiff diff = mock(FileDiff.class);
     when(diff.getBlocks()).thenReturn(blocks);
     FileDiffList diffList = new FileDiffList();
-    Whitebox.setInternalState(diffList, "diffs", new ArrayList<FileDiff>());
+    Whitebox.setInternalState(diffList, "diffs", new DiffListByArrayList<>(0));
     @SuppressWarnings("unchecked")
-    ArrayList<FileDiff> diffs = ((ArrayList<FileDiff>)Whitebox.getInternalState
-        (diffList, "diffs"));
-    diffs.add(diff);
+    DiffList<FileDiff> diffs = (DiffList<FileDiff>)Whitebox.getInternalState(
+        diffList, "diffs");
+    diffs.addFirst(diff);
     FileWithSnapshotFeature sf = new FileWithSnapshotFeature(diffList);
     file.addFeature(sf);
   }