--- /dev/null
+#!perl -w
+# Copyright (C) all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+use v5.12; use PublicInbox::TestCommon;
+
+test_lei(sub {
+ ok(!lei('mail-diff', 't/data/0001.patch', 't/data/binary.patch'),
+ 'different messages are different');
+ like($lei_out, qr/^\+/m, 'diff shown');
+ lei_ok('mail-diff', 't/data/0001.patch', 't/data/0001.patch');
+ is($lei_out, '', 'no output if identical');
+});
+
+done_testing;