* TDD for rollbacks

* split upgrade from stable

* trust

* set app data

* not doing upgrade from stable

* bump libjuju for nested assumes in metadata

* test fixes

* get first upgrading unit to check status
* use alternative name for mysql-test-app to avoid confusion with mysql app

* remove dup

* preemptively switchover on completion

* add missing resume

* split to reduce complexity and new mock

* bump lib

* pr feedback

* pr feedback plus more robust test to survice CI

* leader unit will stay in recovery state on rollback

* bump pytest_operator_cache

* fix build_charm fixture return as pathlib.Path

* fix rollback instruction

* address pr comments

* bump upgrade lib

* fix unit test

* more verbosity

* includes upgrade from stable

stable was bumped to version with upgrade support

* fix for rollback (data-platform-libs issue #97)

* extract and use helper function

* unneeded/wrong asserts

* fix fixture

* simplify fixture usage

* another fix

* fix call

* fix fixture reference

* revert mistakenly commited files