Per https://www.mail-archive.com/bug-tar@gnu.org/msg05440.html

diff --git a/tests/difflink.at b/tests/difflink.at
index eadfb08..4e01176 100644
--- a/tests/difflink.at
+++ b/tests/difflink.at
@@ -21,7 +21,7 @@ mkdir a
 genfile -f a/x
 ln -s x a/y
 ln a/y a/z
-tar cf a.tar a
+tar cf a.tar a/x a/y a/z
 rm a/z
 ln -s x a/z
 tar df a.tar