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(%rDeveloper Load/, @logger.logged(:debug).last)
    assert_match(%rSELECT \* 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 are responsible 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 does 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.

Namespace
Methods
S
T
W
Instance Public methods
set_logger(logger)

Overwrite if you use another logger in your log subscriber:

def logger
  ActiveRecord::Base.logger = @logger
end

Source: show | on GitHub 

# File activesupport/lib/active_support/log_subscriber/test_helper.rb, line 96
def set_logger(logger)
  ActiveSupport::LogSubscriber.logger = logger
end
setup()

Source: show | on GitHub 

# File activesupport/lib/active_support/log_subscriber/test_helper.rb, line 36
def setup
  @logger   = MockLogger.new
  @notifier = ActiveSupport::Notifications::Fanout.new

  ActiveSupport::LogSubscriber.colorize_logging = false

  @old_notifier = ActiveSupport::Notifications.notifier
  set_logger(@logger)
  ActiveSupport::Notifications.notifier = @notifier
end
teardown()

Source: show | on GitHub 

# File activesupport/lib/active_support/log_subscriber/test_helper.rb, line 47
def teardown
  set_logger(nil)
  ActiveSupport::Notifications.notifier = @old_notifier
end
wait()

Wait notifications to be published.

Source: show | on GitHub 

# File activesupport/lib/active_support/log_subscriber/test_helper.rb, line 86
def wait
  @notifier.wait
end