Show error banner for one off letter in trial mode

In trial mode you can’t send letters. But it’s still useful to be able
to build up a letter to see how it work.

Best place to put this error is before someone tries to send a letter
for real.

app/templates/partials/check/trying-to-send-letters-in-trial-mode.html

@@ -0,0 +1,8 @@
+<h1 class='banner-title' data-module="track-error" data-error-type="Trying to send letters in trial mode" data-error-label="{{ upload_id }}">
+  You can’t send
+  {{ 'this letter' if count_of_recipients == 1 else 'these letters' }}
+</h1>
+<p>
+  In <a href="{{ url_for('.using_notify') }}#trial-mode">trial mode</a> you
+  can only preview how your letters will look
+</p>

app/templates/views/check/column-errors.html

@@ -109,14 +109,15 @@
 
       {% elif trying_to_send_letters_in_trial_mode %}
 
-        <h1 class='banner-title' data-module="track-error" data-error-type="Trying to send letters in trial mode" data-error-label="{{ upload_id }}">
-          You can’t send
-          {{ 'this letter' if count_of_recipients == 1 else 'these letters' }}
-        </h1>
-        <p>
-          In <a href="{{ url_for('.using_notify') }}#trial-mode">trial mode</a> you
-          can only preview how your letters will look
-        </p>
+        <div class="bottom-gutter">
+          {% with
+            count_of_recipients=count_of_recipients
+          %}
+            {% call banner_wrapper(type='dangerous') %}
+              {% include "partials/check/trying-to-send-letters-in-trial-mode.html" %}
+            {% endcall %}
+          {% endwith %}
+        </div>
 
       {% elif recipients.more_rows_than_can_send %}
 

app/templates/views/notifications/check.html

@@ -7,7 +7,18 @@
 {% endblock %}
 
 {% block maincolumn_content %}
-  {% if error == 'not-allowed-to-send-to' %}
+  {% if template.template_type == 'letter' and current_service.trial_mode %}
+    {% set error = 'trial-mode-letters' %}
+    <div class="bottom-gutter">
+      {% with
+        count_of_recipients=1
+      %}
+        {% call banner_wrapper(type='dangerous') %}
+          {% include "partials/check/trying-to-send-letters-in-trial-mode.html" %}
+        {% endcall %}
+      {% endwith %}
+    </div>
+  {% elif error == 'not-allowed-to-send-to' %}
     <div class="bottom-gutter">
       {% call banner_wrapper(type='dangerous') %}
         {% with

tests/app/main/views/test_send.py

@@ -1976,14 +1976,19 @@ def test_letter_can_only_be_sent_now(
     mocker.patch('app.main.views.send.set_metadata_on_csv_upload')
     mocker.patch('app.main.views.send.get_page_count_for_letter', return_value=1)
 
-    content = client_request.get(
+    page = client_request.get(
         'main.check_messages',
         service_id=SERVICE_ONE_ID,
         upload_id=fake_uuid,
         template_id=fake_uuid,
     )
 
-    assert 'name="scheduled_for"' not in content
+    assert 'name="scheduled_for"' not in page
+    assert normalize_spaces(
+        page.select_one('[type=submit]').text
+    ) == (
+        'Send 1 letter'
+    )
 
 
 @pytest.mark.parametrize('when', [
@@ -2761,6 +2766,51 @@ def test_one_off_letters_have_download_link(
     assert page.select_one('a[download]').text == 'Download as a printable PDF'
 
 
+def test_send_one_off_letter_errors_in_trial_mode(
+    client_request,
+    mocker,
+    mock_get_service,
+    mock_get_service_letter_template,
+    mock_has_permissions,
+    fake_uuid,
+    mock_get_users_by_service,
+    mock_get_service_statistics,
+    mock_get_job_doesnt_exist,
+    mock_s3_set_metadata,
+):
+
+    mocker.patch(
+        'app.main.views.send.get_page_count_for_letter',
+        return_value=5,
+    )
+
+    with client_request.session_transaction() as session:
+        session['recipient'] = None
+        session['placeholders'] = {
+            'address_line_1': 'First Last',
+            'address_line_2': '123 Street',
+            'postcode': 'SW1 1AA',
+        }
+
+    page = client_request.get(
+        'main.check_notification',
+        service_id=SERVICE_ONE_ID,
+        template_id=fake_uuid,
+        _test_page_title=False,
+    )
+
+    assert normalize_spaces(page.select('.banner-dangerous')) == normalize_spaces(
+        'You can’t send this letter '
+        'In trial mode you can only preview how your letters will look'
+    )
+
+    assert len(page.select('.letter img')) == 5
+
+    assert not page.select('[type=submit]')
+    assert page.select_one('.page-footer-back-link').text == 'Back'
+    assert page.select_one('a[download]').text == 'Download as a printable PDF'
+
+
 def test_check_messages_shows_over_max_row_error(
     logged_in_client,
     api_user_active,