@Test
  public void testCPMutationsAreWrittenToWALEdit() throws Exception {
    createTable(TestMultiMutationCoprocessor.class.getName());

    try (Table t = util.getConnection().getTable(tableName)) {
      t.put(new Put(row1).addColumn(test, dummy, dummy));
      assertRowCount(t, 3);
    }

    assertNotNull(TestWALObserver.savedEdit);
    assertEquals(4, TestWALObserver.savedEdit.getCells().size());
  }
Tests that added mutations from coprocessors end up in the WAL.
hbase-server/src/test/java/org/apache/hadoop/hbase/coprocessor/TestRegionObserverForAddingMutationsFromCoprocessors.java