Flesh out the repository with example and tests

tests/CMakeLists.txt

@@ -0,0 +1,34 @@
+include(FetchContent)
+
+FetchContent_Declare(
+    Unity
+        GIT_REPOSITORY https://github.com/ThrowTheSwitch/Unity.git
+        GIT_TAG v2.6.1
+)
+FetchContent_MakeAvailable(Unity)
+
+add_executable(
+    json_test
+    json_test.c
+)
+set_target_properties(
+    json_test
+    PROPERTIES
+        C_STANDARD 23
+        C_STANDARD_REQUIRED ON
+        C_EXTENSIONS OFF
+)
+target_link_libraries(
+    json_test
+    PRIVATE
+        json
+        unity::framework
+)
+target_include_directories(
+    json_test
+    PRIVATE
+        ${CMAKE_SOURCE_DIR}
+)
+
+add_test(NAME json_test COMMAND json_test)
+