fixes https://github.com/TryGhost/Team/issues/2332
Saves events in the database and collects error information.
Do note that we can emit the same events multiple times, and as a result
out of order. That means we should correctly handle that a delivered
event might be fired after a permanent failure. So a delivered event is
ignored if the email is already marked as failed. Also delivered_at is
reset to null when we receive a permanent failure.
- during a refactor, I moved the `BATCH_SIZE` variable around
- putting the variable export above a more general export means it get
overwritten and the value is `undefined` outside of the module
- when we chunk the emails, we were chunking in sized of `undefined`,
so I'm guessing it just defaulted to 1
- this means the email batches were of size 1 instead of 1000 - oops
- some of the existing tests return `items` as an empty array
- the upcoming change to switch `mailgun-js` to `mailgun.js` means it's
more strict about requiring `paging` too
- this commit adds a new empty-response fixture so we can standardize
using that across tests
- this is the current functionality of the code, as it has always been,
but this test ensures we prioritise the values in the config over
those in settings
refs https://github.com/TryGhost/Toolbox/issues/363
- this copies over tests from `email-analytics-provider-mailgun` that
are more relevant here
- there is now duplication in tests across the two packages but this
will be resolved soon
- this test checks that the mailgun client respects the changes in
settings, which is something that we used to ask
`email-analytics-provider-mailgun` to do when the mailgun client was
made in that package
- since then, we've pulled it out, so we should move the test to the
`mailgun-client` library
refs https://github.com/TryGhost/Toolbox/issues/363
- this commit pulls all code involving the Mailgun client SDK into one
new package called `mailgun-client`
- this means we should be able to replace `mailgun-js` (deprecated) with
`mailgun.js` (the new, official one) without editing code all over the
place
- this also lays some groundwork for better testing of smaller
components
