def METHOD_NAME():
    county_data = {CommonFields.NEW_CASES: [1, 2, 3], CommonFields.STAFFED_BEDS: [5, 10, 20]}
    data = {
        Region.from_fips("34001"): county_data,
        Region.from_fips("34009"): county_data,
        Region.from_fips("36035"): county_data,
        Region.from_cbsa_code("11100"): {
            CommonFields.NEW_CASES: [2, 3, 4],
            CommonFields.STAFFED_BEDS: [30, 40, 50],
        },
        Region.from_state("MA"): {
            CommonFields.NEW_CASES: [10, 20, 30],
            CommonFields.STAFFED_BEDS: [50, 100, 200],
        },
    }
    dataset_in = test_helpers.build_dataset(data)
    aggregator = statistical_areas.CountyToHSAAggregator.from_local_data()
    ds_out = aggregator.aggregate(
        dataset_in=dataset_in,
        fields_to_aggregate={CommonFields.STAFFED_BEDS: CommonFields.STAFFED_BEDS_HSA},
    )
    county_data[CommonFields.STAFFED_BEDS_HSA] = [10, 20, 40]
    expected = test_helpers.build_dataset(
        {
            **data,
            Region.from_fips("36035"): {
                CommonFields.NEW_CASES: [1, 2, 3],
                CommonFields.STAFFED_BEDS: [5, 10, 20],
                CommonFields.STAFFED_BEDS_HSA: [5, 10, 20],
            },
            # New county is added b/c it's in the same HSA as 36035, so the HSA data is carried over
            Region.from_fips("36057"): {CommonFields.STAFFED_BEDS_HSA: [5, 10, 20]},
        }
    )
    test_helpers.assert_dataset_like(ds_out, expected)