[patch v3 6/6] test: add broken roundtrip test

[David Bremner]

david at tethera.net writes:
> +     # delete every second tag
> +     notmuch tag $(notmuch search --output=tags '*' | \
> +	 awk '{ if (NR % 2 == 0) printf " -'%s'", $1 }')  '*'

replaced in git with the less flaky:

     notmuch tag +this_tag_is_very_unlikely_to_be_random '*'

Since the only point is to show the restore fails, adding tags works as
well as deleting them.

d