We previously decided against this [^1] but the lambda alerts are
not a replacement for this one.
Even if both sets of alerts go off, we expect PagerDuty to aggregate
them into a single notification.
[^1]: 65c21f694c
The new alert happens earlier but is otherwise the same:
- We only create a ticket in Production.
- We only create a ticket on approval.
I took this opportunity to refactor the alert as a private function
and test this specifically in detail to avoid lots of repetitive
mocks, which are required when calling the main "update" function.
One test I haven't preserved was for when the "names" array is empty,
as this was added for a legacy data integrity scenario [^1].
[^1]: bf0bf4e31c
This is because that function is used both when broadcast status
is updated via API and via admin, so it's a shared resource.
Also move and update tests for updating broadcast message status
so things are tested at source and repetition is avoided.
