[Justice] Update test_custom_child_agency_name test to remove redun…

…dancies and improve readability (Recidiviz/recidiviz-data#29595)

## Description of the change

Updates `test_custom_child_agency_name` based upon the suggestion of
Michelle in [this PR
](Recidiviz/recidiviz-data#29571 was
merged before I was able to address her feedback).

## Checklists

### Development

**This box MUST be checked by the submitter prior to merging**:
- [x] **Double- and triple-checked that there is no Personally
Identifiable Information (PII) being mistakenly added in this pull
request**

These boxes should be checked by the submitter prior to merging:
- [x] Tests have been written to cover the code changed/added as part of
this pull request

### Code review

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- [ ] This pull request has a descriptive title and information useful
to a reviewer
- [ ] Potential security implications or infrastructural changes have
been considered, if relevant

GitOrigin-RevId: 4c3e467c81df6715a4bf2e72ee12bf880cc5bcbb

recidiviz/tests/justice_counts/spreadsheet_test.py

@@ -408,7 +408,9 @@ def test_custom_child_agency_name(self) -> None:
                 agency_id=agency.id,
             )
             session.add(spreadsheet)
-            # Excel workbook will have an invalid sheet.
+            # Excel workbook will not have any warnings or errors.
+            # create_excel_file is populating the agency name with the custom_child_agency_name.
+
             file_path = create_excel_file(
                 system=schema.System.PRISONS,
                 file_name="test_custom_child_agency_name.xlsx",
@@ -434,11 +436,18 @@ def test_custom_child_agency_name(self) -> None:
                 upload_filetype=BulkUploadFileType.XLSX,
             )
 
-            spreadsheet = session.query(schema.Spreadsheet).one()
             spreadsheet = session.query(schema.Spreadsheet).one()
             self.assertEqual(spreadsheet.status, schema.SpreadsheetStatus.INGESTED)
             self.assertEqual(spreadsheet.ingested_by, user.auth0_user_id)
+
             # Confirm that datapoints were ingested for the child agency
+            child_agency_datapoints = []
+            for datapoint_json_list in metric_key_to_datapoint_jsons.values():
+                child_agency_datapoints += [
+                    datapoint_json
+                    for datapoint_json in datapoint_json_list
+                    if datapoint_json["agency_name"] == child_agency.name
+                ]
 
             self.assertTrue(
                 len(list(itertools.chain(*metric_key_to_datapoint_jsons.values()))) > 0