Since version 3.2 there is a new test_get_user_notification_preferences in source message/tests/externallib_test.php.
It seems to check if there is exactly 8 notifications providers. I suppose those providers come with Moodle application.
We developed and added a custom notification provider to our Moodle application.
So when the test is running, it find 9 providers instead of 8 and test fails.

It is possible to change the way test is done?
One solution would be to check there is at least 8 providers.
Other solution would be to check using the provider's names that all providers that come with Moodle are there.