feat: add byte order mark to talpa export for better excel support

backend/benefit/applications/services/csv_export_base.py

@@ -130,6 +130,10 @@ def get_csv_string_lines_generator(
         io = StringIO()
         csv_writer = csv.writer(io, delimiter=self.CSV_DELIMITER, quoting=quoting)
         line_length_set = set()
+
+        # Add BOM as the first item in the generator
+        yield '\ufeff'
+
         for line in self.get_csv_cell_list_lines_generator():
             line_length_set.add(len(line))
             assert len(line_length_set) == 1, "Each CSV line must have same colum count"

backend/benefit/applications/tests/test_talpa_integration.py

@@ -101,6 +101,9 @@ def test_talpa_csv_date(pruned_applications_csv_service_with_one_application):
     )
     assert csv_lines[1][12] == '"2021-08-27"'
 
+def _has_bom(filename):
+    with open(filename, 'rb') as f:
+        return f.read(3) == b'\xef\xbb\xbf'
 
 def test_write_talpa_csv_file(
     pruned_applications_csv_service_with_one_application, tmp_path
@@ -112,7 +115,9 @@ def test_write_talpa_csv_file(
     application.save()
     output_file = tmp_path / "output.csv"
     pruned_applications_csv_service_with_one_application.write_csv_file(output_file)
-    with open(output_file, encoding="utf-8") as f:
+    with open(output_file, encoding="utf-8-sig") as f:
         contents = f.read()
         assert contents.startswith('"Hakemusnumero";"Työnantajan tyyppi"')
         assert "äöÄÖtest" in contents
+
+    assert _has_bom(output_file)