$ hg init

  $ echo a > a

  $ hg commit -A -ma

  adding a

  $ echo b >> a

  $ hg commit -mb

  $ echo c >> a

  $ hg commit -mc

  $ hg up 1

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

  $ echo d >> a

  $ hg commit -md

  created new head

  $ hg up 1

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

  $ echo e >> a

  $ hg commit -me

  created new head

  $ hg up 1

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

Should fail because not at a head:

  $ hg merge

  abort: branch 'default' has 3 heads - please merge with an explicit rev

  (run 'hg heads .' to see heads)

  [255]

  $ hg up

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

Should fail because > 2 heads:

  $ HGMERGE=internal:other; export HGMERGE

  $ hg merge

  abort: branch 'default' has 3 heads - please merge with an explicit rev

  (run 'hg heads .' to see heads)

  [255]

Should succeed:

  $ hg merge 2

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

  (branch merge, don't forget to commit)

  $ hg commit -mm1

Should succeed - 2 heads:

  $ hg merge -P

  changeset:   3:ea9ff125ff88

  parent:      1:1846eede8b68

  user:        test

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

  summary:     d

  $ hg merge

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

  (branch merge, don't forget to commit)

  $ hg commit -mm2

Should fail because at tip:

  $ hg merge

  abort: there is nothing to merge

  [255]

  $ hg up 0

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

Should fail because there is only one head:

  $ hg merge

  abort: there is nothing to merge - use "hg update" instead

  [255]

  $ hg up 3

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

  $ echo f >> a

  $ hg branch foobranch

  marked working directory as branch foobranch

  $ hg commit -mf

Should fail because merge with other branch:

  $ hg merge

  abort: branch 'foobranch' has one head - please merge with an explicit rev

  (run 'hg heads' to see all heads)

  [255]

Test for issue2043: ensure that 'merge -P' shows ancestors of 6 that

are not ancestors of 7, regardless of where their least common

ancestor is.

Merge preview not affected by common ancestor:

  $ hg up -q 7

  $ hg merge -q -P 6

  2:2d95304fed5d

  4:f25cbe84d8b3

  5:a431fabd6039

  6:e88e33f3bf62