id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
25647	Regression with TEST MIRROR database migrations	Gavin Wahl	nobody	"I have a project with two databases: 'default' and 'logging', where logging is just an alias for default (to allow writing to logging while in a transaction in default). I have logging has `'TEST': {'MIRROR': 'default'}`, and a database router that doesn't allow migrating on logging.

When running the tests, migrations randomly fail to run. This is because `get_unique_databases` stores all the aliases for a specific database in a set, and then `setup_databases` migrates on the 'first' one, despite sets not having a 'first' element. This randomly, based on hash randomization in python, picks either 'default' or 'logging' to be migrated. When 'logging' is migrated, all the migrations are no-ops because migrating is turned off for 'logging'.

I believe this is a regression introduced in 49eee8424."	Bug	new	Testing framework	1.8	Normal				Unreviewed	0	0	0	0	0	0