@Test
  public void testLoadRegionFromMetaRegionNotInMeta() throws Exception {
    try {
      this.util.startMiniCluster();
      final AssignmentManager am = this.util.getHBaseCluster().getMaster().getAssignmentManager();
      final TableName tableName = TableName.valueOf("testLoadRegionFromMetaRegionNotInMeta");
      this.util.createTable(tableName, "f");
      final RegionInfo hri = createRegionInfo(tableName, 1);
      assertNull("Bogus RegionInfo discovered in RegionStates.",
        am.getRegionStates().getRegionState(hri));
      am.populateRegionStatesFromMeta(hri.getEncodedName());
      assertNull("RegionInfo was never added in META", am.getRegionStates().getRegionState(hri));
    } finally {
      this.util.killMiniHBaseCluster();
    }
  }
It is possible that when AM send assign meta request to a RS successfully, but RS can not send
back any response, which cause master startup hangs forever
hbase-server/src/test/java/org/apache/hadoop/hbase/master/assignment/TestAssignmentManager.java