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    * Licensed to the Apache Software Foundation (ASF) under one
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    * distributed with this work for additional information
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    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
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    *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
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   * See the License for the specific language governing permissions and
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  package org.apache.hadoop.hbase.replication.regionserver;
  
  import static org.junit.Assert.assertEquals;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.fs.Path;
  import org.apache.hadoop.hbase.HBaseConfiguration;
  import org.apache.hadoop.hbase.testclassification.ReplicationTests;
  import org.apache.hadoop.hbase.testclassification.SmallTests;
  import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
  import org.apache.hadoop.hbase.util.ManualEnvironmentEdge;
  import org.junit.Test;
  import org.junit.experimental.categories.Category;
  
  @Category({SmallTests.class,ReplicationTests.class})
  public class TestReplicationSourceLogQueue {
  
    /*
      Testing enqueue and dequeuing of wal and check age of oldest wal.
    */
    @Test
    public void testEnqueueDequeue() {
      try {
        String walGroupId1 = "fake-walgroup-id-1";
        String walGroupId2 = "fake-walgroup-id-2";
  
        ManualEnvironmentEdge manualEdge = new ManualEnvironmentEdge();
        EnvironmentEdgeManager.injectEdge(manualEdge);
  
        MetricsSource metrics = new MetricsSource("1");
        Configuration conf = HBaseConfiguration.create();
        ReplicationSourceLogQueue logQueue = new ReplicationSourceLogQueue(conf, metrics);
        final Path log1 = new Path("log-walgroup-a.8");
        manualEdge.setValue(10);
        // Diff of current time (10) and  log-walgroup-a.8 timestamp will be 2.
        logQueue.enqueueLog(log1, walGroupId1);
        assertEquals(2, logQueue.getOldestWalAge());
  
        final Path log2 = new Path("log-walgroup-b.4");
        // Diff of current time (10) and log-walgroup-b.4 will be 6 so oldestWalAge should be 6
        logQueue.enqueueLog(log2, walGroupId2);
        assertEquals(6, logQueue.getOldestWalAge());
  
        // Remove an element from walGroupId2.
        // After this op, there will be only one element in the queue log-walgroup-a.8
        logQueue.remove(walGroupId2);
        assertEquals(2, logQueue.getOldestWalAge());
  
        // Remove last element from the queue.
        logQueue.remove(walGroupId1);
        // This will test the case where there are no elements in the queue.
        assertEquals(0, logQueue.getOldestWalAge());
      } finally {
        EnvironmentEdgeManager.reset();
      }
    }
  }