Extend existing tests

Author: lucic71

tests/unit/chrono_day_conversion.cpp

@@ -1,9 +1,14 @@
-// ADDITIONAL_COMPILE_FLAGS: -std=c++17
+// ADDITIONAL_COMPILE_FLAGS: -std=c++20
 #include <assert.h>
+#include <chrono>
 #include <filesystem>
 #include <string>
 
 int main() {
+  unsigned n = 17;
+  std::chrono::day d(n);
+  assert(static_cast<unsigned>(d) == 17);
+
   const char *name = "dir/file.txt";
   std::filesystem::path p(name);
   std::string s = static_cast<std::string>(p);