From: Tanaka Akira <akr@...>
Date: 2008-10-18T10:50:04+09:00
Subject: [ruby-core:19373] capture_io in minitest

capture_io changes $stdout.fileno.

It changes puts behavior in child process of IO.popen("-").

In the following test, test_popen fails if test_cap runs
first.

% cat zc.rb                         
require 'minitest/unit'

class TestCap < MiniTest::Unit::TestCase
  def test_cap
    out, err = capture_io { puts "foo" }
    assert_equal("foo\n", out)
    assert_equal(1, $stdout.fileno)
  end

  def test_popen
    res = IO.popen("-") {|io|
      if io
        # parent
        io.read
      else
        # child
        puts "bar"
      end
    }
    assert_equal("bar\n", res)
  end
end

MiniTest::Unit.autorun
% ./ruby zc.rb -v                   
Loaded suite zc
Started
TestCap#test_cap: 0.00 s: F
TestCap#test_popen: bar
0.00 s: F

Finished in 0.008575 seconds.

  1) Failure:
test_cap(TestCap) [zc.rb:7]:
Expected 1, not 3.

  2) Failure:
test_popen(TestCap) [zc.rb:20]:
Expected "bar\n", not "".

2 tests, 3 assertions, 2 failures, 0 errors, 0 skips

The problem is caused by capture_io restores $stdout as
dupped $stdout.

% svn diff --diff-cmd diff -x -u lib/minitest/unit.rb
Index: lib/minitest/unit.rb
===================================================================
--- lib/minitest/unit.rb	(revision 19827)
+++ lib/minitest/unit.rb	(working copy)
@@ -191,7 +191,7 @@
     def capture_io
       require 'stringio'
 
-      orig_stdout, orig_stderr         = $stdout.dup, $stderr.dup
+      orig_stdout, orig_stderr         = $stdout, $stderr
       captured_stdout, captured_stderr = StringIO.new, StringIO.new
       $stdout, $stderr                 = captured_stdout, captured_stderr
 
-- 
Tanaka Akira