Latest version of Rails contains compatibility fixes for Ruby 2.7 and some
minor security fixes we would like to have
It also broke some of the multisite tests.
Rails tries to use the same connection for reading from a replica as writing
to the leader during tests, because, with everything happening in a
transaction, changes to the DB wouldn't otherwise be reflected in the
replica connection.
The difference now is that Rails tries to do this for connections opened
after the test has started which affected rails multisite connections.
The upshot of this is that, as things stand, you are likely to
experience problems if you try to connect to a different multisite DB in
a test when the `current_db` is not 'default'.
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