Add task to send canary to cbc proxy

Create and schedule a Celery task that tests if we
can send a canary message to cbc proxy.

This will help us know if something happens to our
connection to cbc proxy.

Signed-off-by: Toby Lorne <toby.lornewelch-richards@digital.cabinet-office.gov.uk>
Co-authored-by: Pea <pea.tyczynska@digital.cabinet-office.gov.uk>
Co-authored-by: Richard <richard.baker@digital.cabinet-office.gov.uk>

tests/app/celery/test_scheduled_tasks.py

@@ -1,3 +1,4 @@
+import uuid
 from datetime import datetime, timedelta
 from unittest.mock import call
 
@@ -555,3 +556,22 @@ def test_check_for_services_with_high_failure_rates_or_sending_to_tv_numbers(
         subject="[test] High failure rates for sms spotted for services",
         ticket_type='incident'
     )
+
+
+def test_send_canary_to_cbc_proxy_invokes_cbc_proxy_client(
+    mocker,
+):
+    mock_send_canary = mocker.patch(
+        'app.cbc_proxy_client.send_canary',
+    )
+
+    scheduled_tasks.send_canary_to_cbc_proxy()
+
+    mock_send_canary.assert_called
+    # the 0th argument of the call to send_canary
+    identifier = mock_send_canary.mock_calls[0][1][0]
+
+    try:
+        uuid.UUID(identifier)
+    except BaseException:
+        pytest.fail(f"{identifier} is not a valid uuid")