perf-test: emacs tagging

Time tag operations, to see if it is worthwhile keeping both the
batch and the non-batch calls to notmuch tag.

performance-test/T06-emacs.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+test_description='emacs operations'
+
+. $(dirname "$0")/perf-test-lib.sh || exit 1
+. $NOTMUCH_SRCDIR/test/test-lib-emacs.sh || exit 1
+
+test_require_emacs
+
+time_start
+
+print_emacs_header
+
+MSGS=$(notmuch search --output=messages "*" | shuf -n 50 | awk '{printf " \"%s\"",$1}')
+
+time_emacs "tag messages" \
+"(dolist (msg (list $MSGS))
+   (notmuch-tag msg (list \"+test\"))
+   (notmuch-tag msg (list \"-test\"))))"
+
+time_done