tests: need to include unistd.h to get usleep.
diff --git a/tests/test-publish-async.cpp b/tests/test-publish-async.cpp
index e8031b0..4b18f20 100644
--- a/tests/test-publish-async.cpp
+++ b/tests/test-publish-async.cpp
@@ -8,6 +8,7 @@
 #include <sstream>
 #include <iostream>
 #include <time.h>
+#include <unistd.h>
 #include <ndn-cpp/face.hpp>
 #include <ndn-cpp/security/identity/memory-identity-storage.hpp>
 #include <ndn-cpp/security/identity/memory-private-key-storage.hpp>