Create a repository:

  $ hg init t

  $ cd t

Make a changeset:

  $ echo a > a

  $ hg add a

  $ 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 ui, hg, commands

  > myui = ui.ui()

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

  > commands.update(myui, repo, rev=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

  1 files, 1 changesets, 1 total revisions

At the end...