def METHOD_NAME():
    age_40s = DemographicBucket("age:40-49")
    metrics_before = {
        CommonFields.DEATHS: {DemographicBucket.ALL: [0, 1, 1], age_40s: [None, 5, 7]}
    }
    dataset_before = test_helpers.build_default_region_dataset(metrics_before)
    dataset_after = new_cases_and_deaths.add_new_deaths(dataset_before)
    dataset_expected = test_helpers.build_default_region_dataset(
        {
            CommonFields.NEW_DEATHS: {
                DemographicBucket.ALL: [None, 1, 0],
                age_40s: [None, None, 2],
            },
            **metrics_before,
        }
    )
    test_helpers.assert_dataset_like(dataset_after, dataset_expected)