Intercom's database_cleaner setup (supports initial clean, secondary connections, non-transactional tests, and eliminates an unnecessary query)

database_cleaner.rb

require "database_cleaner"
require "database_cleaner/active_record/deletion"

module DatabaseCleaner

  module ActiveRecord
    module SelectiveTruncation

      def information_schema_exists?(_connection)
        true
      end

    end
  end

  # These classes have their own database connections which need to be cleaned.
  # Referencing them here also causes their connection pools to be established,
  # which needs to happen so that a transaction is wrapped around each test.
  SECONDARY_CONNECTIONS = [
    AbstractClownsDatabase,
    AbstractDogsDatabase,
    AbstractWafflesDatabase,
  ].freeze

  def self.strategy_for_example_group(example_group)
    if example_group.use_transactional_tests
      DatabaseCleaner::NullStrategy
    else
      :deletion
    end
  end

  def self.set_active_record_cleaner_strategy(strategy)
    DatabaseCleaner[:active_record].strategy = strategy
    SECONDARY_CONNECTIONS.each do |connection|
      DatabaseCleaner[:active_record, { connection: connection }].strategy = strategy
    end
  end

end

RSpec.configure do |config|
  config.use_transactional_fixtures = true

  config.before(:suite) do
    unless ENV["DATABASE_CLEANER_SKIP_INITIAL_CLEAN"]
      DatabaseCleaner[:active_record].clean_with(:deletion)
    end
  end

  config.before(:each) do |example|
    strategy = DatabaseCleaner.strategy_for_example_group(example.example_group_instance)
    DatabaseCleaner.set_active_record_cleaner_strategy(strategy)
    DatabaseCleaner.start
  end

  config.after(:each) do
    DatabaseCleaner.clean
  end
end