$ cat <<EOF > merge

  > import sys, os

  > 

  > try:

  >     import msvcrt

  >     msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)

  >     msvcrt.setmode(sys.stderr.fileno(), os.O_BINARY)

  > except ImportError:

  >     pass

  > 

  > print "merging for", os.path.basename(sys.argv[1])

  > EOF

  $ HGMERGE="python ../merge"; export HGMERGE

  $ mkdir t

  $ cd t

  $ hg init

  $ echo This is file a1 > a

  $ hg add a

  $ hg commit -m "commit #0"

  $ echo This is file b1 > b

  $ hg add b

  $ hg commit -m "commit #1"

  $ hg update 0

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

  $ echo This is file c1 > c

  $ hg add c

  $ hg commit -m "commit #2"

  created new head

  $ echo This is file b1 > b

no merges expected

  $ hg merge -P 1

  changeset:   1:b8bb4a988f25

  user:        test

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

  summary:     commit #1

  $ hg merge 1

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

  (branch merge, don't forget to commit)

  $ hg diff --nodates

  diff -r 49035e18a8e6 b

  --- /dev/null

  +++ b/b

  @@ -0,0 +1,1 @@

  +This is file b1

  $ hg status

  M b

  $ cd ..; rm -r t

  $ mkdir t

  $ cd t

  $ hg init

  $ echo This is file a1 > a

  $ hg add a

  $ hg commit -m "commit #0"

  $ echo This is file b1 > b

  $ hg add b

  $ hg commit -m "commit #1"

  $ hg update 0

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

  $ echo This is file c1 > c

  $ hg add c

  $ hg commit -m "commit #2"

  created new head

  $ echo This is file b2 > b

merge should fail

  $ hg merge 1

  abort: untracked file in working directory differs from file in requested revision: 'b'

merge of b expected

  $ hg merge -f 1

  merging for b

  merging b

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

  (branch merge, don't forget to commit)

  $ hg diff --nodates

  diff -r 49035e18a8e6 b

  --- /dev/null

  +++ b/b

  @@ -0,0 +1,1 @@

  +This is file b2

  $ hg status

  M b

  $ cd ..; rm -r t

  $ mkdir t

  $ cd t

  $ hg init

  $ echo This is file a1 > a

  $ hg add a

  $ hg commit -m "commit #0"

  $ echo This is file b1 > b

  $ hg add b

  $ hg commit -m "commit #1"

  $ echo This is file b22 > b

  $ hg commit -m "commit #2"

  $ hg update 1

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

  $ echo This is file c1 > c

  $ hg add c

  $ hg commit -m "commit #3"

  created new head

Contents of b should be "this is file b1"

  $ cat b

  This is file b1

  $ echo This is file b22 > b

merge fails

  $ hg merge 2

  abort: outstanding uncommitted changes (use 'hg status' to list changes)

  $ echo %% merge expected!

  %% merge expected!

  $ hg merge -f 2

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

  (branch merge, don't forget to commit)

  $ hg diff --nodates

  diff -r 85de557015a8 b

  --- a/b

  +++ b/b

  @@ -1,1 +1,1 @@

  -This is file b1

  +This is file b22

  $ hg status

  M b

  $ cd ..; rm -r t

  $ mkdir t

  $ cd t

  $ hg init

  $ echo This is file a1 > a

  $ hg add a

  $ hg commit -m "commit #0"

  $ echo This is file b1 > b

  $ hg add b

  $ hg commit -m "commit #1"

  $ echo This is file b22 > b

  $ hg commit -m "commit #2"

  $ hg update 1

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

  $ echo This is file c1 > c

  $ hg add c

  $ hg commit -m "commit #3"

  created new head

  $ echo This is file b33 > b

merge of b should fail

  $ hg merge 2

  abort: outstanding uncommitted changes (use 'hg status' to list changes)

merge of b expected

  $ hg merge -f 2

  merging for b

  merging b

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

  (branch merge, don't forget to commit)

  $ hg diff --nodates

  diff -r 85de557015a8 b

  --- a/b

  +++ b/b

  @@ -1,1 +1,1 @@

  -This is file b1

  +This is file b33

  $ hg status

  M b