Make text message price dependent on date

So we don’t have to deploy a change on a Saturday.

In the future this could pull from the rates in the database, but while
that code is shifting around I didn’t want to touoch it. We’d also have
to think about caching so as not to have a non-authenticated route
hitting the database.

tests/app/main/views/test_index.py

@@ -356,3 +356,36 @@ def test_font_preload(
     for element in preload_tags:
         assert element['href'].startswith('https://static.example.com/fonts/')
         assert element['href'].endswith('.woff2')
+
+
+@pytest.mark.parametrize('current_date, expected_rate', (
+    ('2022-04-30', '1.61'),
+    ('2022-05-01', '1.72'),
+))
+def test_sms_price(
+    client_request,
+    mock_get_service_and_organisation_counts,
+    current_date,
+    expected_rate,
+):
+    client_request.logout()
+
+    with freeze_time(current_date):
+        home_page = client_request.get('main.index', _test_page_title=False)
+        pricing_page = client_request.get('main.pricing')
+
+    assert normalize_spaces(
+        home_page.select('.product-page-section')[5].select('.govuk-grid-column-one-half')[1].text
+    ) == (
+        f'Text messages '
+        f'Up to 40,000 free text messages a year, '
+        f'then {expected_rate} pence per message'
+    )
+
+    assert normalize_spaces(
+        pricing_page.select_one('#text-messages + p + p').text
+    ) == (
+        f'When a service has used its annual allowance, it costs '
+        f'{expected_rate} pence (plus VAT) for each text message you '
+        f'send.'
+    )