--- a/tests/test-graft.t Sun Feb 07 22:18:24 2016 -0800
+++ b/tests/test-graft.t Mon Feb 08 18:29:17 2016 +0900
@@ -1,3 +1,9 @@
+ $ cat >> $HGRCPATH <<EOF
+ > [defaults]
+ > # for portability
+ > extdiff = --option -Nru
+ > EOF
+
Create a repo with some stuff in it:
$ hg init a