Fix https://github.com/google/kati/issues/46
diff --git a/testcase/append_self_reference.mk b/testcase/append_self_reference.mk
new file mode 100644
index 0000000..8f3912f
--- /dev/null
+++ b/testcase/append_self_reference.mk
@@ -0,0 +1,8 @@
+x := one
+x += two $(x)
+$(info $(x))
+
+# TODO: shouldn't crash.
+#y = one
+#y += two $(y)
+#$(info $(y))
\ No newline at end of file