Fix warnings in test code
Fix warnings in test code

Signed/unsigned comparison

otris/ews-cpp,bkircher/ews-cpp,otris/ews-cpp,m-Schlitzer/ews-cpp,otris/ews-cpp,bkircher/ews-cpp,m-Schlitzer/ews-cpp,m-Schlitzer/ews-cpp,bkircher/ews-cpp,otris/ews-cpp