Improved CMake structure.

tests/CMakeLists.txt

@@ -2,7 +2,7 @@ set(target tests)
 
 file(GLOB core_sources "*.cpp")
 
-include_directories(
+set(includes
 	${Boost_INCLUDE_DIRS}
 	${PROJECT_SOURCE_DIR}/include
 	${PROJECT_SOURCE_DIR}/lib/catch/single_include
@@ -14,6 +14,7 @@ set(libraries
 )
 
 add_executable(${target} ${core_sources})
+target_include_directories(${target} PRIVATE ${includes})
 target_link_libraries(${target} ${libraries})
 
 add_custom_target(run-tests