Tighten check for reply to address conflict error

The check was made more permissive temporarily as we were changing
error code we are returning form API from 400 to 409.

app/main/views/service_settings.py

@@ -391,7 +391,7 @@ def service_add_email_reply_to(service_id):
                 service_id, form.email_address.data
             )["data"]["id"]
         except HTTPError as e:
-            if e.status_code == 409 or e.status_code == 400:
+            if e.status_code == 409:
                 flash(e.message, 'error')
                 return redirect(url_for('.service_email_reply_to', service_id=service_id))
             else:
@@ -518,7 +518,7 @@ def service_edit_email_reply_to(service_id, reply_to_email_id):
                 service_id, form.email_address.data
             )["data"]["id"]
         except HTTPError as e:
-            if e.status_code == 400 or e.status_code == 409:
+            if e.status_code == 409:
                 flash(e.message, 'error')
                 return redirect(url_for('.service_email_reply_to', service_id=service_id))
             else:

tests/app/main/views/test_service_settings.py

@@ -1,6 +1,6 @@
 from datetime import datetime
 from functools import partial
-from unittest.mock import ANY, PropertyMock, call
+from unittest.mock import ANY, Mock, PropertyMock, call
 from urllib.parse import parse_qs, urlparse
 from uuid import UUID, uuid4
 
@@ -8,6 +8,7 @@ import pytest
 from bs4 import BeautifulSoup
 from flask import url_for
 from freezegun import freeze_time
+from notifications_python_client.errors import HTTPError
 from notifications_utils.clients.zendesk.zendesk_client import ZendeskClient
 
 import app
@@ -2524,6 +2525,48 @@ def test_edit_reply_to_email_address_goes_straight_to_update_if_address_not_chan
     mock_verify.assert_not_called()
 
 
+@pytest.mark.parametrize('url', [
+    'main.service_edit_email_reply_to',
+    'main.service_add_email_reply_to',
+])
+def test_add_edit_reply_to_email_address_goes_straight_to_update_if_address_not_changed(
+    mocker,
+    fake_uuid,
+    client_request,
+    mock_update_reply_to_email_address,
+    url
+):
+    reply_to_email_address = create_reply_to_email_address()
+    mocker.patch('app.service_api_client.get_reply_to_email_addresses', return_value=[reply_to_email_address])
+    mocker.patch('app.service_api_client.get_reply_to_email_address', return_value=reply_to_email_address)
+    error_message = 'Your service already uses ‘reply_to@example.com’ as an email reply-to address.'
+    mocker.patch(
+        'app.service_api_client.verify_reply_to_email_address', side_effect=[HTTPError(
+            response=Mock(
+                status_code=409,
+                json={
+                    'result': 'error',
+                    'message': error_message
+                }
+            ),
+            message=error_message
+        )]
+    )
+    data = {"is_default": "y", 'email_address': "reply_to@example.com"}
+    page = client_request.post(
+        url,
+        service_id=SERVICE_ONE_ID,
+        reply_to_email_id=fake_uuid,
+        _data=data,
+        _follow_redirects=True
+    )
+
+    assert page.find('h1').text == "Reply-to email addresses"
+    assert error_message in page.find('div', class_='banner-dangerous').text
+
+    mock_update_reply_to_email_address.assert_not_called()
+
+
 @pytest.mark.parametrize('reply_to_address, expected_link_text, partial_href', [
     (
         create_reply_to_email_address(is_default=False),