Make sure tests can be run offline and by adding new cmake switch

Author: Gianfranco Costamagna

cmake/download_test_data.cmake

@@ -1,14 +1,19 @@
 set(JSON_TEST_DATA_URL     https://github.com/nlohmann/json_test_data)
 set(JSON_TEST_DATA_VERSION 3.1.0)
 
-include(ExternalProject)
+set(JSON_TEST_DATA_DIR /usr/share/json_test_data-${JSON_TEST_DATA_VERSION})
+
+if(EXISTS ${JSON_TEST_DATA_DIR})
+  set(JSON_TestDataDirectory ${JSON_TEST_DATA_DIR})
+endif()
 
 # if variable is set, use test data from given directory rather than downloading them
 if(JSON_TestDataDirectory)
     message(STATUS "Using test data in ${JSON_TestDataDirectory}.")
     add_custom_target(download_test_data)
     file(WRITE ${CMAKE_BINARY_DIR}/include/test_data.hpp "#define TEST_DATA_DIRECTORY \"${JSON_TestDataDirectory}\"\n")
 else()
+    include(ExternalProject)
     # create a header with the path to the downloaded test data
     file(WRITE ${CMAKE_BINARY_DIR}/include/test_data.hpp "#define TEST_DATA_DIRECTORY \"${CMAKE_BINARY_DIR}/test_files\"\n")
 

tests/CMakeLists.txt

@@ -192,6 +192,9 @@ if (JSON_Install)
 endif()
 
 add_subdirectory(cmake_add_subdirectory)
-add_subdirectory(cmake_fetch_content)
-add_subdirectory(cmake_fetch_content2)
+if (NOT JSON_No_Internet)
+    add_subdirectory(cmake_fetch_content)
+    add_subdirectory(cmake_fetch_content2)
+endif()
+
 add_subdirectory(cmake_target_include_directories)