@Test
  public void testConstantSizePolicy() throws IOException {
    TableDescriptor td = TableDescriptorBuilder.newBuilder(TABLENAME).setMaxFileSize(1024L).build();
    doReturn(td).when(mockRegion).getTableDescriptor();
    ConstantSizeRegionSplitPolicy policy =
      (ConstantSizeRegionSplitPolicy) RegionSplitPolicy.create(mockRegion, conf);
    doConstantSizePolicyTests(policy);
  }
Test setting up a customized split policy
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestRegionSplitPolicy.java