Fix the test_suite by using catch’s single_include directory

CMakeLists.txt

@@ -308,7 +308,7 @@ set_target_properties(catch PROPERTIES EXCLUDE_FROM_ALL TRUE)
 ExternalProject_Get_Property(catch SOURCE_DIR)
 if(NOT EXISTS ${CMAKE_SOURCE_DIR}/tests/catch.hpp)
   target_include_directories(test_suite
-    PUBLIC "${SOURCE_DIR}/include/"
+    PUBLIC "${SOURCE_DIR}/single_include/"
     )
   add_dependencies(test_suite catch)
 endif()

tests/network.cpp

@@ -1,5 +1,6 @@
 #include "catch.hpp"
 #include <network/tls_policy.hpp>
+#include <sstream>
 
 #ifdef BOTAN_FOUND
 TEST_CASE("tls_policy")