public Set<String> getColumnNames() {
    if (_segment == null) {
      throw new IllegalStateException("Index segment for Lazy row is uninitialized.");
    }
    return _segment.getColumnNames();
  }
@Test
  public void testGetColumnNames() {
    IndexSegment segment = getMockSegment();
    LazyRow lazyRow = new LazyRow();
    lazyRow.init(segment, 1);
    HashSet<String> columnNames = new HashSet<>(Arrays.asList("col1", "col2"));
    when(segment.getColumnNames()).thenReturn(columnNames);

    assertEquals(lazyRow.getColumnNames(), columnNames);
  }