cmake: add import config tests

test/cmake_add_subdirectory/project/CMakeLists.txt

@@ -0,0 +1,13 @@
+cmake_minimum_required(VERSION 3.8)
+
+project(DummyImport CXX)
+
+set(JSON_BuildTests OFF CACHE INTERNAL "")
+add_subdirectory(${nlohmann_json_source}
+   ${CMAKE_CURRENT_BINARY_DIR}/nlohmann_json)
+
+add_executable(with_namespace_target main.cpp)
+target_link_libraries(with_namespace_target nlohmann_json::nlohmann_json)
+
+add_executable(without_namespace_target main.cpp)
+target_link_libraries(without_namespace_target nlohmann_json)

test/cmake_add_subdirectory/project/main.cpp

@@ -0,0 +1,8 @@
+#include <nlohmann/json.hpp>
+
+int main(int argc, char **argv)
+{
+    nlohmann::json j;
+
+    return 0;
+}