refactor: rename testbench to test.

- rename testbench to test.
- add benchmark for future development.

test/main.cpp

@@ -0,0 +1,6 @@
+#include <gtest/gtest.h>
+
+int main(int argc, char* argv[]) {
+    testing::InitGoogleTest(&argc, argv);
+    return RUN_ALL_TESTS();
+}