Mark test/suffix_subst as failing
diff --git a/test/suffix_subst.mk b/test/suffix_subst.mk
index 9cd9927..8858b3d 100644
--- a/test/suffix_subst.mk
+++ b/test/suffix_subst.mk
@@ -1,3 +1,5 @@
+# TODO
+
 foo:= hoge.c
 
 test: