Test: unsigned_underflow.cpp
unsigned_underflow.cpp:2:1: error: 'size_t' does not name a type
    2 | size_t available() const {
      | ^~~~~~
unsigned_underflow.cpp:1:1: note: 'size_t' is defined in header '<cstddef>'; did you forget to '#include <cstddef>'?
  +++ |+#include <cstddef>
    1 | // Ring buffer - fix underflow bug in available()