Correct description of how service name appears

This has changed since we made prefixing text messages its own setting.

tests/app/main/views/test_service_settings.py

@@ -236,16 +236,27 @@ def test_escapes_letter_contact_block(
 
 
 def test_should_show_service_name(
-        logged_in_client,
-        service_one,
+    client_request,
 ):
-    response = logged_in_client.get(url_for(
-        'main.service_name_change', service_id=service_one['id']))
-    assert response.status_code == 200
-    page = BeautifulSoup(response.data.decode('utf-8'), 'html.parser')
+    page = client_request.get('main.service_name_change', service_id=SERVICE_ONE_ID)
     assert page.find('h1').text == 'Change your service name'
     assert page.find('input', attrs={"type": "text"})['value'] == 'service one'
-    app.service_api_client.get_service.assert_called_with(service_one['id'])
+    assert page.select_one('main p').text == 'Users will see your service name:'
+    assert normalize_spaces(page.select_one('main ul').text) == (
+        'at the start of every text message, eg ‘service one: This is an example message’ '
+        'as your email sender name'
+    )
+    app.service_api_client.get_service.assert_called_with(SERVICE_ONE_ID)
+
+
+def test_should_show_service_name_with_no_prefixing(
+    client_request,
+    service_one,
+):
+    service_one['prefix_sms'] = False
+    page = client_request.get('main.service_name_change', service_id=SERVICE_ONE_ID)
+    assert page.find('h1').text == 'Change your service name'
+    assert page.select_one('main p').text == 'Users will see your service name as your email sender name.'
 
 
 def test_should_redirect_after_change_service_name(