tests: fix warnings

While I don't see -Werror being used on tests anytime soon, there's no
reason to keep the warnings in tests unfixed.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/tests/heavy-wq.c b/tests/heavy-wq.c
index e5f688c..2f133cc 100644
--- a/tests/heavy-wq.c
+++ b/tests/heavy-wq.c
@@ -36,6 +36,8 @@
 #include "workqueue.h"
 #include <math.h>
 
+#include "tests.h"
+
 extern struct thread_master *master;
 static struct work_queue *heavy_wq;