Ensure trial mode error overrides too many rows

Telling users that they can’t send to more than 50 recipients in trial
mode doesn’t apply for letters (they can’t send to _any_ recipients).

So we should make sure that the error message about not being able to
send to any recipients always comes up instead of the 50 recipients one,
whether you’re trying to upload a file with 1 or 111 rows.

tests/app/main/views/test_send.py

@@ -1583,6 +1583,10 @@ def test_check_messages_shows_trial_mode_error(
     (mock_get_service, True),
     (mock_get_live_service, False),
 ])
+@pytest.mark.parametrize('number_of_rows, expected_error_message', [
+    (1, 'You can’t send this letter'),
+    (111, 'You can’t send these letters'),
+])
 def test_check_messages_shows_trial_mode_error_for_letters(
     client_request,
     api_user_active,
@@ -1593,14 +1597,16 @@ def test_check_messages_shows_trial_mode_error_for_letters(
     mocker,
     service_mock,
     error_should_be_shown,
+    number_of_rows,
+    expected_error_message,
 ):
 
     service_mock(mocker, api_user_active)
 
-    mocker.patch('app.main.views.send.s3download', return_value='''
-        address_line_1,address_line_2,postcode,
-        First Last,    123 Street,    SW1 1AA
-    ''')
+    mocker.patch('app.main.views.send.s3download', return_value='\n'.join(
+        ['address_line_1,address_line_2,postcode,'] +
+        ['First Last,    123 Street,    SW1 1AA'] * number_of_rows
+    ))
 
     with client_request.session_transaction() as session:
         session['upload_data'] = {'template_id': ''}
@@ -1617,10 +1623,10 @@ def test_check_messages_shows_trial_mode_error_for_letters(
 
     if error_should_be_shown:
         assert normalize_spaces(error[0].text) == (
-            'You can’t send this letter '
+            '{} '
             'In trial mode you can only preview how your letters will look '
             'Skip to file contents'
-        )
+        ).format(expected_error_message)
     else:
         assert not error
 
@@ -1668,7 +1674,7 @@ def test_non_ascii_characters_in_letter_recipients_file_shows_error(
     api_user_active,
     mock_login,
     mock_get_users_by_service,
-    mock_get_service,
+    mock_get_live_service,
     mock_has_permissions,
     mock_get_service_letter_template,
     mock_get_detailed_service_for_today,