@Override
  public String getString(int rowIndex, int columnIndex) {
    if (columnIndex != 0) {
      throw new IllegalArgumentException("Column index must always be 0 for aggregation result sets");
    }

    if (rowIndex != 0) {
      throw new IllegalArgumentException("Row index must always be 0 for aggregation result sets");
    }

    return _jsonObject.get("value").asText();
  }
@Test
  public void testGetString() {
    // Run the test
    final String result = _aggregationResultSetUnderTest.getString(0, 0);

    // Verify the results
    assertEquals("123", result);
  }