Allow tests to be ignored (#12)

CMakeLists.txt

@@ -5,11 +5,13 @@ project(tracelogging)
 include(GNUInstallDirs)
 
 add_compile_options(-Wall -Wextra -Werror)
+set(TRACELOGGING_BUILD_TESTS ON CACHE BOOL "Build tests.")
 
 # Include source
 add_subdirectory(src)
 
 # Only include testing stuff if we are the top level
+if(TRACELOGGING_BUILD_TESTS)
     if (${CMAKE_PROJECT_NAME} STREQUAL ${PROJECT_NAME})
         enable_testing()
 
@@ -20,3 +22,4 @@ if (${CMAKE_PROJECT_NAME} STREQUAL ${PROJECT_NAME})
 
         add_subdirectory(test)
     endif ()
+endif ()