Testing with RSpec that a method uses the right DB replica

I want to setup a test that checks for a given method that that method will use the right replica role (using the Multiple Database feature by ActiveSupport since Rails 6.1)

Let's pretend that we have this database configuration:

# config/database.yml
default: &default
  # (omissis)

test:
  primary:
    <<: *default
    database: primary_db
  primary_replica:
    <<: *default
    database: reader_db # for testing purpose, could be the same primary_db...
    replica: true

the default writing and reading database roles that Rails conventionally would expect to be present and this class:

class MyService
  def call_to_primary
    Model.where(id: 1)
  end

  def call_to_reader
    ActiveRecord::Base.connected_to(role: :reading) do
      Model.where(id: 1)
    end
  end
end

I want to write a test to check that all the methods in the class above are using the reader replica and thus I'll expect that the test on the call_to_primary method will fail, while the test on the call_to_reader won't.

What is the right/best way to achieve this in RSpec?

Thank you!