--- a/tests/test-diff-unified	Thu Nov 27 16:07:17 2008 +0100
+++ b/tests/test-diff-unified	Thu Nov 27 17:00:54 2008 +0100
@@ -44,6 +44,15 @@
 echo '% invalid diff.unified'
 hg --config diff.unified=foo diff --nodates
 
-exit 0
+echo % test off-by-one error with diff -p
+hg init diffp
+cd diffp
+echo a > a
+hg ci -Ama
+rm a
+echo b > a
+echo a >> a
+echo c >> a
+hg diff -U0 -p
 
-
+exit 0