From: Alexey Verkhovsky <alex_verk@...>
Date: 2004-04-03T04:06:17+09:00
Subject: [newbie] assert_writes implementation

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.

Here is my code:

   def assert_writes(expectedOutput)
     reader, writer = IO.pipe

     if fork
       begin
         writer.close
         output = reader.read
       ensure
         reader.close if (reader && !reader.closed?)
       end
       Process.wait
       assert_equal(expectedOutput, output)
     else
       begin
         reader.close
         yield(writer)
       ensure
         writer.close if (writer && !writer.closed?)
       end
     end
   end

   # usage example
   def test_display
     assert_writes("aaa") {|outputStream| "aaa".display(outputStream)}
   end

Please be so kind to tell me:

1. Is it normal to do it this way?

2. Is it the right way to do it? I am not sure this code handles all 
exception paths correctly.

3. Rdoc says that "IO#pipe" is not supported on all platforms. So, is 
there a portable way to do it?

Brgds,
Alexey Verkhovsky