test: add test for checking forwarded messages

Add test of forwarding messages from within emacs.
The first test checks that a references header is properly
added to the new message.  The second test checks that the
send-hook of the forwarding message adds a forwarded-tag
to the original message.

test/T730-emacs-forwarding.sh

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+
+test_description="emacs forwarding"
+. $(dirname "$0")/test-lib.sh || exit 1
+
+test_begin_subtest "Forward setting the correct references header"
+# Check that, when forwarding a message, the new message has
+# a References-header pointing to the original (forwarded) message.
+
+message_id='OriginalMessage@notmuchmail.org'
+add_message \
+    [id]="$message_id" \
+    '[from]="user@example.com"' \
+    '[subject]="This is the original message"' \
+    '[body]="Dummy text."'
+
+test_emacs_expect_t "
+  (let ((message-send-mail-function (lambda () t)))
+    (notmuch-show \"id:$message_id\")
+    (notmuch-show-forward-message)
+    (save-restriction
+      (message-narrow-to-headers)
+      (message-remove-header \"Fcc\")
+      (message-remove-header \"To\")
+      (message-add-header \"To: nobody@example.com\"))
+
+    (notmuch-mua-send)
+    (notmuch-test-expect-equal
+        (message-field-value \"References\") \"<$message_id>\"))
+"
+
+test_begin_subtest "Forwarding adding the forwarded tag"
+# Check that sending the forwarding message in the previous
+# subtest did add the forwarded-tag to the message that was forwarded.
+
+test_expect_equal "$(notmuch search --output=tags id:$message_id | sort)" \
+"forwarded
+inbox
+unread"
+
+test_done