Implicit requirement due to use of std::setw

diff --git a/devapi/tests/session-t.cc b/devapi/tests/session-t.cc
index 758a0b8f..138cdcac 100644
--- a/devapi/tests/session-t.cc
+++ b/devapi/tests/session-t.cc
@@ -35,6 +35,7 @@
 #include <thread>
 #include <map>
 #include <sstream>
+#include <iomanip>
 
 using std::cout;
 using std::endl;