diff --git a/CMakeLists.txt b/CMakeLists.txt
index dd53f99..51db36f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,14 +1,13 @@
 # See the end of this file for copyright and license terms.
 
-cmake_minimum_required(VERSION 3.0.0)
-project(neo VERSION 0.1.0 LANGUAGES C ASM)
+cmake_minimum_required(VERSION 3.14.0)
+project(neo VERSION 0.1.0 LANGUAGES C)
 set(CMAKE_C_STANDARD 11)
+set(CMAKE_C_EXTENSIONS ON)
 
 if(CMAKE_PROJECT_NAME STREQUAL PROJECT_NAME)
     set_property(GLOBAL PROPERTY USE_FOLDERS ON)
     option(DEBUG "Enable debug features" ON)
-    include(CTest)
-    enable_testing()
 endif()
 
 find_package(Git QUIET)
@@ -29,6 +28,12 @@ add_subdirectory(src)
 
 add_subdirectory(demo)
 
+option(BUILD_TESTING "Build tests" ON)
+if((CMAKE_PROJECT_NAME STREQUAL PROJECT_NAME OR NEO_BUILD_TESTING) AND BUILD_TESTING)
+    enable_testing()
+    add_subdirectory(test)
+endif()
+
 set(CPACK_PROJECT_NAME ${PROJECT_NAME})
 set(CPACK_PROJECT_VERSION ${PROJECT_VERSION})
 include(CPack)
diff --git a/include/neo/_error.h b/include/neo/_error.h
index b469bb6..fa82702 100644
--- a/include/neo/_error.h
+++ b/include/neo/_error.h
@@ -6,6 +6,7 @@
 extern "C" {
 #endif
 
+#include "neo/_toolchain.h"
 #include "neo/_types.h"
 
 /**
@@ -21,7 +22,7 @@ extern "C" {
  *	the values to insert which will become the error message.
  */
 __attribute__(( __format__(printf, 3, 4) ))
-void yeet(error *err, u32 number, const char *restrict fmt, ...);
+void yeet(error *err, u32 number, const char *__restrict fmt, ...);
 
 /**
  * Indicate an operation has completed successfully.
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
new file mode 100644
index 0000000..608b55f
--- /dev/null
+++ b/test/CMakeLists.txt
@@ -0,0 +1,31 @@
+# See the end of this file for copyright and license terms.
+
+enable_language(CXX)
+set(CMAKE_CXX_STANDARD 17)
+
+include(CTest)
+include(FetchContent)
+FetchContent_Declare(
+    Catch2
+    GIT_REPOSITORY https://github.com/catchorg/Catch2.git
+    GIT_TAG v2.13.6
+)
+FetchContent_MakeAvailable(Catch2)
+
+add_executable(neo_test neo_test.cpp)
+
+target_compile_features(neo_test PRIVATE cxx_std_17)
+target_link_libraries(neo_test PRIVATE neo Catch2::Catch2)
+
+add_test(NAME neo COMMAND neo_test)
+
+# This file is part of libneo.
+# Copyright (c) 2021 Fefie <owo@fef.moe>.
+#
+# libneo is non-violent software: you may only use, redistribute,
+# and/or modify it under the terms of the CNPLv6+ as found in
+# the LICENSE file in the source code root directory or at
+# <https://git.pixie.town/thufie/CNPL>.
+#
+# libneo comes with ABSOLUTELY NO WARRANTY, to the extent
+# permitted by applicable law.  See the CNPLv6+ for details.
diff --git a/test/neo_test.cpp b/test/neo_test.cpp
new file mode 100644
index 0000000..80035ca
--- /dev/null
+++ b/test/neo_test.cpp
@@ -0,0 +1,17 @@
+/** See the end of this file for copyright and license terms. */
+
+#define CATCH_CONFIG_MAIN
+#include <catch2/catch.hpp>
+
+/*
+ * This file is part of libneo.
+ * Copyright (c) 2021 Fefie <owo@fef.moe>.
+ *
+ * libneo is non-violent software: you may only use, redistribute,
+ * and/or modify it under the terms of the CNPLv6+ as found in
+ * the LICENSE file in the source code root directory or at
+ * <https://git.pixie.town/thufie/CNPL>.
+ *
+ * libneo comes with ABSOLUTELY NO WARRANTY, to the extent
+ * permitted by applicable law.  See the CNPLv6+ for details.
+ */