@Override
  public void postPut(final ObserverContext<? extends RegionCoprocessorEnvironment> c,
    final Put put, final WALEdit edit, final Durability durability) throws IOException {
    Map<byte[], List<Cell>> familyMap = put.getFamilyCellMap();
    RegionCoprocessorEnvironment e = c.getEnvironment();
    assertNotNull(e);
    assertNotNull(e.getRegion());
    assertNotNull(familyMap);
    List<Cell> cells = familyMap.get(TestRegionObserverInterface.A);
    if (
      e.getRegion().getTableDescriptor().getTableName()
        .equals(TestRegionObserverInterface.TEST_TABLE)
    ) {
      assertNotNull(cells);
      assertNotNull(cells.get(0));
      // KeyValue v1 expectation. Cast for now until we go all Cell all the time. TODO
      Cell cell = cells.get(0);
      assertTrue(
        Bytes.equals(cell.getQualifierArray(), cell.getQualifierOffset(), cell.getQualifierLength(),
          TestRegionObserverInterface.A, 0, TestRegionObserverInterface.A.length));
      cells = familyMap.get(TestRegionObserverInterface.B);
      assertNotNull(cells);
      assertNotNull(cells.get(0));
      // KeyValue v1 expectation. Cast for now until we go all Cell all the time. TODO
      cell = cells.get(0);
      assertTrue(
        Bytes.equals(cell.getQualifierArray(), cell.getQualifierOffset(), cell.getQualifierLength(),
          TestRegionObserverInterface.B, 0, TestRegionObserverInterface.B.length));
      cells = familyMap.get(TestRegionObserverInterface.C);
      assertNotNull(cells);
      assertNotNull(cells.get(0));
      // KeyValue v1 expectation. Cast for now until we go all Cell all the time. TODO
      cell = cells.get(0);
      assertTrue(
        Bytes.equals(cell.getQualifierArray(), cell.getQualifierOffset(), cell.getQualifierLength(),
          TestRegionObserverInterface.C, 0, TestRegionObserverInterface.C.length));
    }
    ctPostPut.incrementAndGet();
  }
A sample region observer that tests the RegionObserver interface. It works with
TestRegionObserverInterface to provide the test case.
hbase-server/src/test/java/org/apache/hadoop/hbase/coprocessor/SimpleRegionObserver.java