There are at least 3 bugs present.
1) notmuch-show-insert-part-message/rfc822 assumes that message/rfc822
parts will have a ":content" property, but that turns out not to be
the case.
2) something deep in gnus wants gnus-newsgroup-charset, but that is
defined in gnus-sum, which is not loaded by default.
3) If gnus-sum is loaded, then the display of the message/rfc822 part
succeeds, but the buffer gets put into gnus-article-mode, which means
that, inter alia, notmuch text properties and keybindings get wiped.
(test-visible-output)'
test_expect_equal_file $EXPECTED/notmuch-show-decrypted-message OUTPUT
+test_begin_subtest "show encrypted rfc822 message"
+test_subtest_known_broken
+test_emacs '(notmuch-show "id:encrypted-rfc822-attachment@crypto.notmuchmail.org")
+ (test-visible-output)'
+test_expect_code 1 'fgrep "!!!" OUTPUT'
+
test_begin_subtest "show undecryptable message"
test_emacs '(notmuch-show "id:simple-encrypted@crypto.notmuchmail.org")
(test-visible-output)'