Cache broadcast messages in Redis

This should make the pages slightly quicker to load, because Redis will
return the JSON string faster than the API.

The only change that can happen to a broadcast which doesn’t go through
the admin app is a broadcast ending at its scheduled time. So this could
result in a cached broadcast having a status of `broadcasting` when it
had in fact finished. We already account for this here though:
b2b58ec044/app/models/broadcast_message.py (L89-L94)

tests/app/notify_client/test_broadcast_message_client.py

@@ -0,0 +1,92 @@
+from app.notify_client.broadcast_message_api_client import (
+    BroadcastMessageAPIClient,
+)
+
+
+def test_create_broadcast_message(mocker):
+    client = BroadcastMessageAPIClient()
+    mocker.patch('app.notify_client.current_user', id='1')
+    mock_post = mocker.patch(
+        'app.notify_client.broadcast_message_api_client.BroadcastMessageAPIClient.post'
+    )
+    client.create_broadcast_message(
+        service_id='12345',
+        template_id='67890',
+    )
+    mock_post.assert_called_once_with(
+        '/service/12345/broadcast-message',
+        data={
+            'service_id': '12345',
+            'template_id': '67890',
+            'personalisation': {},
+            'created_by': '1',
+        },
+    )
+
+
+def test_get_broadcast_messages(mocker):
+    client = BroadcastMessageAPIClient()
+    mock_get = mocker.patch(
+        'app.notify_client.broadcast_message_api_client.BroadcastMessageAPIClient.get'
+    )
+    client.get_broadcast_messages('12345')
+    mock_get.assert_called_once_with(
+        '/service/12345/broadcast-message',
+    )
+
+
+def test_get_broadcast_message(mocker):
+    client = BroadcastMessageAPIClient()
+    mocker.patch('app.notify_client.current_user', id='1')
+    mock_get = mocker.patch(
+        'app.notify_client.broadcast_message_api_client.BroadcastMessageAPIClient.get',
+        return_value={'abc': 'def'},
+    )
+    mock_redis_set = mocker.patch('app.extensions.RedisClient.set')
+    client.get_broadcast_message(service_id='12345', broadcast_message_id='67890')
+    mock_get.assert_called_once_with(
+        '/service/12345/broadcast-message/67890',
+    )
+    mock_redis_set.assert_called_once_with(
+        'broadcast-message-67890',
+        '{"abc": "def"}',
+        ex=604_800,
+    )
+
+
+def test_update_broadcast_message(mocker):
+    client = BroadcastMessageAPIClient()
+    mocker.patch('app.notify_client.current_user', id='1')
+    mock_post = mocker.patch(
+        'app.notify_client.broadcast_message_api_client.BroadcastMessageAPIClient.post'
+    )
+    mock_redis_delete = mocker.patch('app.extensions.RedisClient.delete')
+    client.update_broadcast_message(
+        service_id='12345',
+        broadcast_message_id='67890',
+        data={'abc': 'def'},
+    )
+    mock_post.assert_called_once_with(
+        '/service/12345/broadcast-message/67890',
+        data={'abc': 'def'},
+    )
+    mock_redis_delete.assert_called_once_with('broadcast-message-67890')
+
+
+def test_update_broadcast_message_status(mocker):
+    client = BroadcastMessageAPIClient()
+    mocker.patch('app.notify_client.current_user', id='1')
+    mock_post = mocker.patch(
+        'app.notify_client.broadcast_message_api_client.BroadcastMessageAPIClient.post'
+    )
+    mock_redis_delete = mocker.patch('app.extensions.RedisClient.delete')
+    client.update_broadcast_message_status(
+        'cancelled',
+        service_id='12345',
+        broadcast_message_id='67890',
+    )
+    mock_post.assert_called_once_with(
+        '/service/12345/broadcast-message/67890/status',
+        data={'created_by': '1', 'status': 'cancelled'},
+    )
+    mock_redis_delete.assert_called_once_with('broadcast-message-67890')