aruba_extension.rb

module MyFancyTool
  module TestSupport
    module ArubaExt
      
      def with_redirected_stdout(&block)
        redirect_stdout
        yield
        bring_back_stdout
      end
 
      def mock_stdout
        unescape @stdout_cache
      end
 
      def mock_stderr
        unescape @stderr_cache
      end
 
      def mock_output
        mock_stdout + mock_stderr
      end
 
      private
 
      def redirect_stdout
        @stdout_cache = ''
        @stderr_cache = ''
 
        @stdout_redirected = true
        @orig_stdout = $stdout
        @orig_stderr = $stderr
        $stdout = @mock_stdout = StringIO.new
        $stderr = @mock_stderr = StringIO.new
      end
 
      def bring_back_stdout
        @stdout_cache = @mock_stderr.string
        @stderr_cache = @mock_stdout.string
 
        @stdout_redirected = false
        $stdout = @orig_stdout
        $stderr = @orig_stderr
        @orig_stdout = @mock_stdout = nil
        @orig_stderr = @mock_stderr = nil
      end
    end
  end
end
 
World(MyFancyTool::TestSupport::ArubaExt)

basic_steps.rb

When /^I run my fancy tool with command "(.*)"$/ do |args|
  args = args.split
  args[0] = args[0].to_sym
 
  Dir.chdir(current_dir) do
    with_redirected_stdout do
      MyFancyTool::MyCLI.start args
    end
  end
end
 
Then /^the last output should match (#{PATTERN})$/ do |expected|
  assert { mock_output =~ expected }
end

example.feature

Feature: Reassuring awesomeness of MyFancyTool.
 
Scenario: Running the tool
  When I run my fancy tool with command "do stuff"
  Then the last output should match /awesome output/