Rails horizontal sharding doesn't work with unknown shard argument error on rails 6.1.7.2

Question

I've implemented simple horizontal sharding in a rails application. There are 2 shards: Primary, and shard_one.

When running in test environment,

I've set up a super simple test in a global setup in test_helper.rb to test this:

    ActiveRecord::Base.connected_to(shard: :primary, role: :reading) do
      p Tenant.count
    end

    ActiveRecord::Base.connected_to(shard: :shard_one, role: :reading) do
      p Tenant.count
    end

The output of which is

ArgumentError: unknown keyword: :shard

The databases exist, migrations run successfully. No problems with the configurations.

So there's definitely some sort of initialization not running for the test runner, but I don't know what it is.

The application configuration is :

test:
  primary:
    <<: *default
    url: <%= ENV['TEST_DATABASE_URL'] %>
  shard_one:
    <<: *default
    url: <%= ENV['TEST_ARCHIVE_DATABASE_URL'] %>

class ApplicationRecord < RxModule::ApplicationRecord
  self.abstract_class = true
  connects_to shards: {
    primary: { writing: :primary, reading: :primary },
    archive: { writing: :shard_one, reading: :shard_one }
  }
end

Does anyone have any insight here?

I tried api ActiveRecord::Base.connected_to?(shard: :primary, role: :reading), and it works as expected. Without shard parameter, it works too. And I even drill down to /var/lib/gems/2.7.0/gems/activerecord-6.1.7.2/lib/active_record/connection_handling.rb and confirm the api contains shard parameter.