t / t4101 / diff.1-2on commit contrib/subtree: better error handling for 'subtree add' (10a4958)
   1--- a/frotz
   2+++ b/frotz
   3@@ -1,3 +1,2 @@
   4 a
   5-b
   6-c
   7+b
   8\ No newline at end of file