Leaking state and non-obvious order (before :all runs *before* RailsHelper.test_setup) are not worth it.
A replacement PR for #13370. Fixes some flaky specs, e.g.
```
bin/rspec './spec/components/freedom_patches/translate_accelerator_spec.rb[1:3]' './spec/jobs/clean_up_user_export_topics_spec.rb[1:1]' --tag ~type:multisite --seed 35994
```
Also included:
* DEV: No need for locale reset (we do it anyway in rails_helper in `test_setup`)
Extracted commonly used spec helpers into spec/support/uploads_helpers.rb, removed unused stubs and let definitions. Makes it easier to write new S3-related specs without copy and pasting setup steps from other specs.
* DEV: new S3 backup layout
Currently, with $S3_BACKUP_BUCKET of "bucket/backups", multisite backups
end up in "bucket/backups/backups/dbname/" and single-site will be in
"bucket/backups/".
Both _should_ be in "bucket/backups/dbname/"
- remove MULTISITE_PREFIX,
- always include dbname,
- method to move to the new prefix
- job to call the method
* SPEC: add tests for `VacateLegacyPrefixBackups` onceoff job.
Co-authored-by: Vinoth Kannan <vinothkannan@vinkas.com>
