bookmark: introduce in advance a variant of the exchange test
We are about to introduce a new way to push bookmark to server. We introduce
the test variant before actually updating the exchange to help the output
changes to stand out when it happens.
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