Create a repository:

#if no-extraextensions

  $ hg config

  devel.all-warnings=true

  devel.default-date=0 0

  extensions.fsmonitor= (fsmonitor !)

  largefiles.usercache=$TESTTMP/.cache/largefiles

  lfs.usercache=$TESTTMP/.cache/lfs

  ui.slash=True

  ui.interactive=False

  ui.detailed-exit-code=True

  ui.merge=internal:merge

  ui.mergemarkers=detailed

  ui.promptecho=True

  web.address=localhost

  web\.ipv6=(?:True|False) (re)

  web.server-header=testing stub value

#endif

  $ hg init t

  $ cd t

Prepare a changeset:

  $ echo a > a

  $ hg add a

  $ hg status

  A a

Writes to stdio succeed and fail appropriately

#if devfull

  $ hg status 2>/dev/full

  A a

  $ hg status >/dev/full

  abort: No space left on device

  [255]

#endif

#if devfull

  $ hg status >/dev/full 2>&1

  [255]

  $ hg status ENOENT 2>/dev/full

  [255]

#endif

  $ hg commit -m test

This command is ancient:

  $ hg history

  changeset:   0:acb14030fe0a

  tag:         tip

  user:        test

  date:        Thu Jan 01 00:00:00 1970 +0000

  summary:     test

Verify that updating to revision 0 via commands.update() works properly

  $ cat <<EOF > update_to_rev0.py

  > from mercurial import commands, hg, ui as uimod

  > myui = uimod.ui.load()

  > repo = hg.repository(myui, path=b'.')

  > commands.update(myui, repo, rev=b"0")

  > EOF

  $ hg up null

  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ "$PYTHON" ./update_to_rev0.py

  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg identify -n

  0

Poke around at hashes:

  $ hg manifest --debug

  b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 644   a

  $ hg cat a

  a

Verify should succeed:

  $ hg verify

  checking changesets

  checking manifests

  crosschecking files in changesets and manifests

  checking files

  checked 1 changesets with 1 changes to 1 files

Repository root:

  $ hg root

  $TESTTMP/t

  $ hg log -l1 -T '{reporoot}\n'

  $TESTTMP/t

  $ hg root -Tjson | sed 's|\\\\|\\|g'

  [

   {

    "hgpath": "$TESTTMP/t/.hg",

    "reporoot": "$TESTTMP/t",

    "storepath": "$TESTTMP/t/.hg/store"

   }

  ]

At the end...

  $ cd ..

Status message redirection:

  $ hg init empty

 status messages are sent to stdout by default:

  $ hg outgoing -R t empty -Tjson 2>/dev/null

  comparing with empty

  searching for changes

  [

   {

    "bookmarks": [],

    "branch": "default",

    "date": [0, 0],

    "desc": "test",

    "node": "acb14030fe0a21b60322c440ad2d20cf7685a376",

    "parents": ["0000000000000000000000000000000000000000"],

    "phase": "draft",

    "rev": 0,

    "tags": ["tip"],

    "user": "test"

   }

  ]

 which can be configured to send to stderr, so the output wouldn't be

 interleaved:

  $ cat <<'EOF' >> "$HGRCPATH"

  > [ui]

  > message-output = stderr

  > EOF

  $ hg outgoing -R t empty -Tjson 2>/dev/null

  [

   {

    "bookmarks": [],

    "branch": "default",

    "date": [0, 0],

    "desc": "test",

    "node": "acb14030fe0a21b60322c440ad2d20cf7685a376",

    "parents": ["0000000000000000000000000000000000000000"],

    "phase": "draft",

    "rev": 0,

    "tags": ["tip"],

    "user": "test"

   }

  ]

  $ hg outgoing -R t empty -Tjson >/dev/null

  comparing with empty

  searching for changes

 this option should be turned off by HGPLAIN= since it may break scripting use:

  $ HGPLAIN= hg outgoing -R t empty -Tjson 2>/dev/null

  comparing with empty

  searching for changes

  [

   {

    "bookmarks": [],

    "branch": "default",

    "date": [0, 0],

    "desc": "test",

    "node": "acb14030fe0a21b60322c440ad2d20cf7685a376",

    "parents": ["0000000000000000000000000000000000000000"],

    "phase": "draft",

    "rev": 0,

    "tags": ["tip"],

    "user": "test"

   }

  ]

 but still overridden by --config:

  $ HGPLAIN= hg outgoing -R t empty -Tjson --config ui.message-output=stderr \

  > 2>/dev/null

  [

   {

    "bookmarks": [],

    "branch": "default",

    "date": [0, 0],

    "desc": "test",

    "node": "acb14030fe0a21b60322c440ad2d20cf7685a376",

    "parents": ["0000000000000000000000000000000000000000"],

    "phase": "draft",

    "rev": 0,

    "tags": ["tip"],

    "user": "test"

   }

  ]

Invalid ui.message-output option:

  $ hg log -R t --config ui.message-output=bad

  abort: invalid ui.message-output destination: bad

  [255]

Underlying message streams should be updated when ui.fout/ferr are set:

  $ cat <<'EOF' > capui.py

  > from mercurial import pycompat, registrar

  > cmdtable = {}

  > command = registrar.command(cmdtable)

  > @command(b'capui', norepo=True)

  > def capui(ui):

  >     out = ui.fout

  >     ui.fout = pycompat.bytesio()

  >     ui.status(b'status\n')

  >     ui.ferr = pycompat.bytesio()

  >     ui.warn(b'warn\n')

  >     out.write(b'stdout: %s' % ui.fout.getvalue())

  >     out.write(b'stderr: %s' % ui.ferr.getvalue())

  > EOF

  $ hg --config extensions.capui=capui.py --config ui.message-output=stdio capui

  stdout: status

  stderr: warn