ActiveSupport::LogSubscriber::TestHelper

Provides some helpers to deal with testing log subscribers by setting up notifications. Take for instance Active Record subscriber tests:

  class SyncLogSubscriberTest < ActiveSupport::TestCase
    include ActiveSupport::LogSubscriber::TestHelper

    def setup
      ActiveRecord::LogSubscriber.attach_to(:active_record)
    end

    def test_basic_query_logging
      Developer.all
      wait
      assert_equal 1, @logger.logged(:debug).size
      assert_match /Developer Load/, @logger.logged(:debug).last
      assert_match /SELECT \* FROM "developers"/, @logger.logged(:debug).last
    end
  end

All you need to do is to ensure that your log subscriber is added to Rails::Subscriber, as in the second line of the code above. The test helpers is reponsible for setting up the queue, subscriptions and turning colors in logs off.

The messages are available in the @logger instance, which is a logger with limited powers (it actually do not send anything to your output), and you can collect them doing @logger.logged(level), where level is the level used in logging, like info, debug, warn and so on.