Test git-patch-id

So far, git-patch-id was untested.  Add some simple checks for output
format and patch (in)equality.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4203-patch-id.sh

@@ -0,0 +1,38 @@
+#!/bin/sh
+
+test_description='git patch-id'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit initial foo a &&
+	test_commit first foo b &&
+	git checkout -b same HEAD^ &&
+	test_commit same-msg foo b &&
+	git checkout -b notsame HEAD^ &&
+	test_commit notsame-msg foo c
+'
+
+test_expect_success 'patch-id output is well-formed' '
+	git log -p -1 | git patch-id > output &&
+	grep "^[a-f0-9]\{40\} $(git rev-parse HEAD)$" output
+'
+
+get_patch_id () {
+	git log -p -1 "$1" | git patch-id |
+		sed "s# .*##" > patch-id_"$1"
+}
+
+test_expect_success 'patch-id detects equality' '
+	get_patch_id master &&
+	get_patch_id same &&
+	test_cmp patch-id_master patch-id_same
+'
+
+test_expect_success 'patch-id detects inequality' '
+	get_patch_id master &&
+	get_patch_id notsame &&
+	! test_cmp patch-id_master patch-id_notsame
+'
+
+test_done