Deal with the fact that user can override stdout/stderr

See #24 for a more thorough description of what's
going on in the matrix

features/regression.feature

@@ -306,3 +306,32 @@ Feature:
 
     # !> world
     """
+
+  Scenario: A program overriding stdout/stderr
+    Given the file "black_hole.rb":
+    """
+    File.open '/dev/null', 'w' do |black_hole|
+      STDERR = $stderr = black_hole
+      STDOUT = $stdout = black_hole
+      puts "You won't see this, it goes into the black hole"
+      system %q(ruby -e '$stdout.puts "stdout gets past it b/c of dumb ruby bug"')
+      system %q(ruby -e '$stderr.puts "stderr gets past it b/c of dumb ruby bug"')
+    end
+    """
+    When I run "seeing_is_believing black_hole.rb"
+    Then stderr is empty
+    And the exit status is 0
+    And stdout is:
+    """
+    File.open '/dev/null', 'w' do |black_hole|                                      # => File
+      STDERR = $stderr = black_hole                                                 # => #<File:/dev/null>
+      STDOUT = $stdout = black_hole                                                 # => #<File:/dev/null>
+      puts "You won't see this, it goes into the black hole"                        # => nil
+      system %q(ruby -e '$stdout.puts "stdout gets past it b/c of dumb ruby bug"')  # => true
+      system %q(ruby -e '$stderr.puts "stderr gets past it b/c of dumb ruby bug"')  # => true
+    end                                                                             # => true
+
+    # >> stdout gets past it b/c of dumb ruby bug
+
+    # !> stderr gets past it b/c of dumb ruby bug
+    """

lib/seeing_is_believing/the_matrix.rb

@@ -10,28 +10,31 @@
 require 'seeing_is_believing/result'
 $SiB = SeeingIsBelieving::Result.new
 
-real_stdout = STDOUT.dup
-real_stderr = STDERR.dup
-read_from_fake_out, write_to_fake_out = IO.pipe
-read_from_fake_err, write_to_fake_err = IO.pipe
+stdout_real_obj = STDOUT      # the real Ruby object, but its FD is going to keep getting reopened
+stderr_real_obj = STDERR
+stdout_real_fd  = STDOUT.dup  # duped Ruby object, but with the real file descriptor
+stderr_real_fd  = STDERR.dup
 
-STDOUT.reopen write_to_fake_out
-STDERR.reopen write_to_fake_err
+read_from_mock_out, write_to_mock_out = IO.pipe
+read_from_mock_err, write_to_mock_err = IO.pipe
+
+stdout_real_obj.reopen write_to_mock_out
+stderr_real_obj.reopen write_to_mock_err
 
 at_exit do
-  STDOUT.reopen real_stdout
-  STDERR.reopen real_stderr
-  write_to_fake_out.close unless write_to_fake_out.closed?
-  write_to_fake_err.close unless write_to_fake_err.closed?
-  $SiB.stdout = read_from_fake_out.read
-  $SiB.stderr = read_from_fake_err.read
-  read_from_fake_out.close
-  read_from_fake_err.close
+  stdout_real_obj.reopen stdout_real_fd
+  stderr_real_obj.reopen stderr_real_fd
+  write_to_mock_out.close unless write_to_mock_out.closed?
+  write_to_mock_err.close unless write_to_mock_err.closed?
+  $SiB.stdout = read_from_mock_out.read
+  $SiB.stderr = read_from_mock_err.read
+  read_from_mock_out.close
+  read_from_mock_err.close
 
   $SiB.exitstatus ||= 0
   $SiB.exitstatus   = 1         if $!
   $SiB.exitstatus   = $!.status if $!.kind_of? SystemExit
   $SiB.bug_in_sib   = $! && ! $!.kind_of?(SystemExit)
 
-  real_stdout.write YAML.dump $SiB
+  stdout_real_fd.write YAML.dump $SiB
 end