From: kwa@... (makotz)
Date: 2003-03-26T09:45:21+09:00
Subject: [Q] changing a stream of 'print' method to a string

Hi,

I have a question.
How to change a stream of 'print' to a string? Is it able?


Background:
I want to test my program which print data to standard output.
And I have no good idea to test output data.

    ----------------------------------------
    ##
    ## main.rb
    ##
    def print_list(list)
      list.each_with_index do |item, index|
        print "#{index+1}: #{item}\n"
      end
    end
    ----------------------------------------
    
    ----------------------------------------
    ##
    ## test program
    ##
    require 'main'
    require 'runit/testcase'
    require 'runit/cui/testrunner'
    
    class MainTest < RUNIT::TestCase
      def test_print_list
        list = [10, 20, 30]
        print_list(list)        # <== how to test?
      end
    end
    
    testcases = MainTest.test_cases()
    RUNIT::CUI::TestRunner.run(testcases)
    ----------------------------------------


If I could change a stream of print to a string, I would write it
like the following:

    ----------------------------------------
      ...(snip)...
    
      def test_print_list
        list = [10, 20, 30]
        expected = <<END
    1: 10
    2: 20
    3: 30
    END
        result = ''
        result << print_list(list)     # if I could
        assert_equal(expected, result)
      end
    
      ...(snip)...
    ----------------------------------------


Please give me an advice.

--
regards,
makotz kuwata