tests/test-dirstate-backup.t

py3: replace file() with open() in test-import-eol.t

file() is not present in Python 3.
This patch also adds b'' prefixes to make sure we write bytes in Python 3.

Differential Revision: https://phab.mercurial-scm.org/D2125

Set up

  $ hg init repo
  $ cd repo

Try to import an empty patch

  $ hg import --no-commit - <<EOF
  > EOF
  applying patch from stdin
  abort: stdin: no diffs found
  [255]

No dirstate backups are left behind

  $ ls .hg/dirstate* | sort
  .hg/dirstate