Added testing with Catch2

CMakeLists.txt

@@ -1,10 +1,30 @@
 cmake_minimum_required(VERSION 3.16)
 project(lispy_stuff)
 
+# we'll use catch2 as testing library.
+include(FetchContent)
+FetchContent_Declare(
+    Catch2
+    GIT_REPOSITORY https://github.com/catchorg/Catch2.git
+    GIT_TAG        v3.8.1
+)
+FetchContent_MakeAvailable(Catch2)
+list(APPEND CMAKE_MODULE_PATH ${catch2_SOURCE_DIR}/extras)
+include(Catch)
+
 set(HEADER_FILES src/include/lex.hpp)
-set(SOURCE_FILES src/main.cpp src/lex.cpp)
+set(SOURCE_FILES src/lex.cpp)
 
+# we're not actually shipping a library yet,
+# this is so we don't have to compile twice for main and tests.
+add_library(libmash STATIC ${SOURCE_FILES} ${HEADER_FILES})
+target_include_directories(libmash PUBLIC src/include/)
 
-add_executable(main ${SOURCE_FILES} ${HEADER_FILES})
+# Main target
+add_executable(main src/main.cpp)
+target_link_libraries(main libmash)
+
+# tests
+add_executable(test src/tests/test.cpp)
+target_link_libraries(test PRIVATE libmash Catch2::Catch2WithMain)
 
-target_include_directories(main PRIVATE src/include/)