t4056: add new tests for "git diff -O"

Adapted from $gmane/236427 by Anders Waldenborg, "diff: Add
diff.orderfile configuration variable".

Signed-off-by: Anders Waldenborg <anders@0x63.nu>
Signed-off-by: Samuel Bronson <naesten@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4056-diff-order.sh

@@ -0,0 +1,68 @@
+#!/bin/sh
+
+test_description='diff order'
+
+. ./test-lib.sh
+
+create_files () {
+	echo "$1" >a.h &&
+	echo "$1" >b.c &&
+	echo "$1" >c/Makefile &&
+	echo "$1" >d.txt &&
+	git add a.h b.c c/Makefile d.txt &&
+	git commit -m"$1"
+}
+
+test_expect_success 'setup' '
+	mkdir c &&
+	create_files 1 &&
+	create_files 2 &&
+
+	cat >order_file_1 <<-\EOF &&
+	*Makefile
+	*.txt
+	*.h
+	EOF
+
+	cat >order_file_2 <<-\EOF &&
+	*Makefile
+	*.h
+	*.c
+	EOF
+
+	cat >expect_none <<-\EOF &&
+	a.h
+	b.c
+	c/Makefile
+	d.txt
+	EOF
+
+	cat >expect_1 <<-\EOF &&
+	c/Makefile
+	d.txt
+	a.h
+	b.c
+	EOF
+
+	cat >expect_2 <<-\EOF
+	c/Makefile
+	a.h
+	b.c
+	d.txt
+	EOF
+'
+
+test_expect_success "no order (=tree object order)" '
+	git diff --name-only HEAD^..HEAD >actual &&
+	test_cmp expect_none actual
+'
+
+for i in 1 2
+do
+	test_expect_success "orderfile using option ($i)" '
+		git diff -Oorder_file_$i --name-only HEAD^..HEAD >actual &&
+		test_cmp expect_$i actual
+	'
+done
+
+test_done