Catch duplicate recipient columns in spreadsheets

If someone has duplicate recipient columns in their file we don’t know
which one to use. This commit adds an error message which should help
them fix the duplication.

This commit doesn’t go to the extra effort to actually show the
correct values for duplication in the preview. Don’t think it’s worth
the effort/complexity for how infrequently we’ve seen this error.

Depends on:
- [ ] https://github.com/alphagov/notifications-utils/pull/376

tests/app/main/views/test_send.py

@@ -421,6 +421,17 @@ def test_upload_csvfile_with_errors_shows_check_page_with_errors(
             'Skip to file contents'
         )
     ),
+    (
+        """
+            phone number, phone number, PHONE_NUMBER
+            +447700900111,+447700900222,+447700900333,
+        """,
+        (
+            'Your file has more than one column called ‘phone number’ or ‘PHONE_NUMBER’ '
+            'Delete or rename one of these columns and try again. '
+            'Skip to file contents'
+        )
+    ),
     (
         """
             phone number, name
@@ -614,6 +625,40 @@ def test_upload_valid_csv_shows_preview_and_table(
         assert normalize_spaces(str(page.select('table tbody td')[index + 1])) == cell
 
 
+def test_show_all_columns_if_there_are_duplicate_recipient_columns(
+    client_request,
+    mocker,
+    mock_get_live_service,
+    mock_get_service_template_with_placeholders,
+    mock_get_users_by_service,
+    mock_get_detailed_service_for_today,
+    fake_uuid,
+):
+
+    with client_request.session_transaction() as session:
+        session['upload_data'] = {'template_id': fake_uuid}
+
+    mocker.patch('app.main.views.send.s3download', return_value="""
+        phone number, phone_number, PHONENUMBER
+        07700900001,  07700900002,  07700900003
+    """)
+
+    page = client_request.get(
+        'main.check_messages',
+        service_id=SERVICE_ONE_ID,
+        template_type='sms',
+        upload_id=fake_uuid,
+        _test_page_title=False,
+    )
+
+    assert normalize_spaces(page.select_one('thead').text) == (
+        'Row in file1 phone number phone_number PHONENUMBER'
+    )
+    assert normalize_spaces(page.select_one('tbody').text) == (
+        '2 07700900003 07700900003 07700900003'
+    )
+
+
 @pytest.mark.parametrize('row_index, expected_status', [
     (0, 404),
     (1, 404),