public HashEntry getHashEntry( Object[] groupData ) {
    return new HashEntry( groupData );
  }
@Test public void hashEntryTest() {
    HashMap<MemoryGroupByData.HashEntry, String> map = new HashMap<>();

    byte[] byteValue1 = "key".getBytes();
    Object[] groupData1 = new Object[1];
    groupData1[0] = byteValue1;

    MemoryGroupByData.HashEntry hashEntry1 = data.getHashEntry( groupData1 );
    map.put( hashEntry1, "value" );

    byte[] byteValue2 = "key".getBytes();
    Object[] groupData2 = new Object[1];
    groupData2[0] = byteValue2;

    MemoryGroupByData.HashEntry hashEntry2 = data.getHashEntry( groupData2 );

    String value = map.get( hashEntry2 );

    assertEquals( "value", value );
  }