Add encode functions to check for NULL output buf and internal error state
diff --git a/test/UsefulBuf_Tests.c b/test/UsefulBuf_Tests.c
index 388f8cf..f53693a 100644
--- a/test/UsefulBuf_Tests.c
+++ b/test/UsefulBuf_Tests.c
@@ -238,6 +238,11 @@
       return "lengths near max size";
    }
 
+   UsefulOutBuf_Init(&UOB, (UsefulBuf){NULL, 100});
+   if(!UsefulOutBuf_IsBufferNULL(&UOB)) {
+      return "NULL check failed";
+   }
+
    return NULL;
 }