https://bz.mercurial-scm.org/1502
Initialize repository
$ hg init foo
$ touch foo/a && hg -R foo commit -A -m "added a"
adding a
$ hg clone foo foo1
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo "bar" > foo1/a && hg -R foo1 commit -m "edit a in foo1"
$ echo "hi" > foo/a && hg -R foo commit -m "edited a foo"
$ hg -R foo1 pull -u
pulling from $TESTTMP/foo (glob)
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
abort: not updating: not a linear update
(merge or update --check to force update)
[255]
$ hg -R foo1 book branchy
$ hg -R foo1 book
* branchy 1:e3e522925eff
Pull. Bookmark should not jump to new head.
$ echo "there" >> foo/a && hg -R foo commit -m "edited a again"
$ hg -R foo1 pull
pulling from $TESTTMP/foo (glob)
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files
(run 'hg update' to get a working copy)
$ hg -R foo1 book
* branchy 1:e3e522925eff