$ hg init a

  $ cd a

  $ echo a > a

  $ hg add -n

  adding a

  $ hg st

  ? a

  $ hg add

  adding a

  $ hg st

  A a

  $ hg forget a

  $ hg add

  adding a

  $ hg st

  A a

  $ echo b > b

  $ hg add -n b

  $ hg st

  A a

  ? b

  $ hg add b

  $ hg st

  A a

  A b

should fail

  $ hg add b

  b already tracked!

  $ hg st

  A a

  A b

  $ hg ci -m 0 --traceback

should fail

  $ hg add a

  a already tracked!

  $ echo aa > a

  $ hg ci -m 1

  $ hg up 0

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

  $ echo aaa > a

  $ hg ci -m 2

  created new head

  $ hg merge

  merging a

  warning: conflicts during merge.

  merging a failed!

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

  use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon

  [1]

  $ hg st

  M a

  ? a.orig

should fail

  $ hg add a

  a already tracked!

  $ hg st

  M a

  ? a.orig

  $ hg resolve -m a

  $ hg ci -m merge

  $ hg forget a

  $ hg add a

  $ hg st

  ? a.orig

  $ hg rm a

  $ hg st

  R a

  ? a.orig

  $ echo a > a

  $ hg add a

  $ hg st

  M a

  ? a.orig

  $ hg add c && echo "unexpected addition of missing file"

  c: No such file or directory

  [1]

  $ echo c > c

  $ hg add d c && echo "unexpected addition of missing file"

  d: No such file or directory

  [1]

  $ hg st

  M a

  A c

  ? a.orig