Thanks to Thomas Schwinge for noticing yet another place where quoting
matters. Since the shell translates \. to ., the regex passed to grep
is too generous without the quotes.
The use of [.] is the suggestion of Tomi Ollila.
# Note, we assume all messages from cworth have a message-id
# containing cworth.org
-grep cworth\.org dump.expected > dump-cworth.expected
+grep 'cworth[.]org' dump.expected > dump-cworth.expected
test_begin_subtest "dump -- from:cworth"
notmuch dump -- from:cworth > dump-dash-cworth.actual