Logger that logs to a string

logger_spec.rb

describe "something with a logger" do
  let(:logger) { TestLogger.new }
  before { Rails.logger = logger }
  
  specify do
    # ... call your code ...
    logger.messages.should include("my message")
  end  
end

test_logger.rb

class TestLogger < Logger
  def initialize
    @strio = StringIO.new
    super(@strio)
  end

  def messages
    @strio.string
  end
end