--- a/tests/test-commandserver.t	Sat Nov 15 13:04:41 2014 +0900
+++ b/tests/test-commandserver.t	Sat Nov 15 13:50:43 2014 +0900
@@ -492,6 +492,7 @@
   foo
 
   $ cat <<EOF > dbgui.py
+  > import os, sys
   > from mercurial import cmdutil, commands
   > cmdtable = {}
   > command = cmdutil.command(cmdtable)
@@ -501,6 +502,14 @@
   > @command("debugprompt", norepo=True)
   > def debugprompt(ui):
   >     ui.write("%s\\n" % ui.prompt("prompt:"))
+  > @command("debugreadstdin", norepo=True)
+  > def debugreadstdin(ui):
+  >     ui.write("read: %r\n" % sys.stdin.read(1))
+  > @command("debugwritestdout", norepo=True)
+  > def debugwritestdout(ui):
+  >     os.write(1, "low-level stdout fd and\n")
+  >     sys.stdout.write("stdout should be redirected to /dev/null\n")
+  >     sys.stdout.flush()
   > EOF
   $ cat <<EOF >> .hg/hgrc
   > [extensions]
@@ -518,10 +527,15 @@
   ...     runcommand(server, ['debugprompt', '--config',
   ...                         'ui.interactive=True'],
   ...                input=cStringIO.StringIO('5678\n'))
+  ...     runcommand(server, ['debugreadstdin'])
+  ...     runcommand(server, ['debugwritestdout'])
   *** runcommand debuggetpass --config ui.interactive=True
   password: 1234
   *** runcommand debugprompt --config ui.interactive=True
   prompt: 5678
+  *** runcommand debugreadstdin
+  read: ''
+  *** runcommand debugwritestdout
 
 
 run commandserver in commandserver, which is silly but should work: