tests/test-nested-repo.t

copies: clarify the return of _merge_copies_dict

I misused that function twice in the past few days, so lets clarify the API.

Differential Revision: https://phab.mercurial-scm.org/D9418

  $ hg init a
  $ cd a
  $ hg init b
  $ echo x > b/x

Should print nothing:

  $ hg add b
  $ hg st

  $ echo y > b/y
  $ hg st

Should fail:

  $ hg st b/x
  abort: path 'b/x' is inside nested repo 'b'
  [255]
  $ hg add b/x
  abort: path 'b/x' is inside nested repo 'b'
  [255]

Should fail:

  $ hg add b b/x
  abort: path 'b/x' is inside nested repo 'b'
  [255]
  $ hg st

Should arguably print nothing:

  $ hg st b

  $ echo a > a
  $ hg ci -Ama a

Should fail:

  $ hg mv a b
  abort: path 'b/a' is inside nested repo 'b'
  [255]
  $ hg st

  $ cd ..