test: modernize style of t4006

Signed-off-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4006-diff-mode.sh

@@ -8,23 +8,21 @@ test_description='Test mode change diffs.
 '
 . ./test-lib.sh
 
-test_expect_success \
-    'setup' \
-    'echo frotz >rezrov &&
-     git update-index --add rezrov &&
-     tree=`git write-tree` &&
-     echo $tree'
+sed_script='s/\(:100644 100755\) \('"$_x40"'\) \2 /\1 X X /'
 
-test_expect_success \
-    'chmod' \
-    'test_chmod +x rezrov &&
-     git diff-index $tree >current'
-
-sed -e 's/\(:100644 100755\) \('"$_x40"'\) \2 /\1 X X /' <current >check
-echo ":100644 100755 X X M	rezrov" >expected
+test_expect_success 'setup' '
+	echo frotz >rezrov &&
+	git update-index --add rezrov &&
+	tree=`git write-tree` &&
+	echo $tree
+'
 
-test_expect_success \
-    'verify' \
-    'test_cmp expected check'
+test_expect_success 'chmod' '
+	test_chmod +x rezrov &&
+	git diff-index $tree >current &&
+	sed -e "$sed_script" <current >check &&
+	echo ":100644 100755 X X M	rezrov" >expected &&
+	test_cmp expected check
+'
 
 test_done