diff --git a/tests/run.rbc b/tests/run.rbc
index 6478159..c7eaf3b 100644
--- a/tests/run.rbc
+++ b/tests/run.rbc
@@ -31,6 +31,9 @@
 assert_eq("", rblf.mkstrip(" \n \t    "))
 assert_eq("a b c", rblf.mkstrip("  a b   \n  c \t"))
 
+assert_eq("b1 b2", rblf.mksubst("a", "b", "a1 a2"))
+assert_eq(["b1", "x2"], rblf.mksubst("a", "b", ["a1", "x2"]))
+
 globals, config = rblf.product_configuration("test/device", init)
 assert_eq(
     {