diff --git a/test/testutils.cpp b/test/testutils.cpp
index 909bc8b7..3383b326 100644
--- a/test/testutils.cpp
+++ b/test/testutils.cpp
@@ -674,6 +674,7 @@ namespace
         assert(s.putchar(0) == false);
         assert(s.putstring("a") == false);
         assert(s.putline("a") == false);
+        assert(s.printf("a") == 0);
         assert(s.getcrc() == 0);
         assert(s.rwops() != nullptr);
         //templates