public static SerializableFunction<Row, TableRow> toTableRow() {
    return ROW_TO_TABLE_ROW;
  }
@Test
  public void testToTableRow_map() {
    TableRow row = toTableRow().apply(MAP_ROW);

    assertThat(row.size(), equalTo(1));
    row = ((List<TableRow>) row.get("map")).get(0);
    assertThat(row.size(), equalTo(2));
    assertThat(row, hasEntry("key", "test"));
    assertThat(row, hasEntry("value", "123.456"));
  }