From: Nathaniel Talbott <nathaniel@...>
Date: 2004-04-03T04:31:56+09:00
Subject: Re: [newbie] assert_writes implementation

On Apr 2, 2004, at 13:06, Alexey Verkhovsky wrote:

> Context: I needed to teach a subclass of Test::Unit::TestCase to 
> assert that a particular block writes something to an output stream.
>
> In Java, an easy way to do something like this is with a pair of 
> PipedOutputStream/PipedInputStream pair. So I tried the same thing in 
> Ruby, and the result looks bit hairy to me. Having to use 
> multi-process semantics to write top a buffer and then read from it is 
> a bit over the top. There must be some better way.

Would StringIO help? 
(http://www.ruby-doc.org/stdlib/libdoc/stringio/rdoc/index.html)

   require 'test/unit'

   require 'stringio'

   class TestAssertWrite < Test::Unit::TestCase
     def assert_write(expected)
       io = StringIO.new
       yield(io)
       assert_equal(expected, io.string)
     end

     def test_assert_write
       assert_raise(Test::Unit::AssertionFailedError) do
         assert_write("expected") do |output|
           output.write("bogus")
         end
       end
       assert_nothing_raised do
         assert_write("expected") do |output|
           output.write("expected")
         end
       end
     end
   end


Nathaniel
Terralien, Inc.

<:((><