Tests for async replication.py (#1033)

* def test_can_promote_cluster():

* test_handle_database_start

* _on_async_relation_changed

* test_on_secret_changed first if

* change a lit bit

* add tests for stop database function

* still need some upgrades

* add this

* add learning

* test__configure_primary_cluster

* clean up

* we don't need import application

* start test__on_async_relation_departed

* format

* done test__on_async_relation_departed

* test_on_async_relation_joined

* test_on_create_replication

* test_promote_to_primary

* add test

* test_wait_for_standby_leader

* formatize

* formatize 2.0

* test_get_partner_addresses

* test_handle_replication_change

* test_handle_forceful_promotion

* add tests

* test_on_async_relation_broken

* formatize

* finishing

* need some help

* date

* add aplications

* format

* promote_standby_cluster is none

* add unit name

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Co-authored-by: Dragomir Penev <[email protected]>

Author: Gere321123