Unittest: Add inventory callback tests

src/unittest/mock_server.h

@@ -17,6 +17,8 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
 
+#pragma once
+
 #include <server.h>
 
 class MockServer : public Server