add_email_corpus itself does an rm -rf $MAIL_DIR, so these are not necessary.
test_expect_equal "$output" "thread:XXX 2001-01-05 [1/1] Notmuch Test Suite; Bears (inbox unread)"
# folder: and path: searches with full corpus
-rm -rf $MAIL_DIR
add_email_corpus
# add some more dupes
test_expect_equal "$output" "thread:XXX 2001-01-05 [1/1] Notmuch Test Suite; To the bone (inbox unread)"
# Use "standard" corpus from here on.
-rm -rf $MAIL_DIR
add_email_corpus
notmuch search --output=messages from:cworth > cworth.msg-ids