Initial unit test submission.

test/date_test/last.pass.cpp

@@ -0,0 +1,16 @@
+// Howard Hinnant
+// This work is licensed under a Creative Commons Attribution 4.0 International License.
+// http://creativecommons.org/licenses/by/4.0/
+
+// constexpr struct last_spec {} last{};
+
+#include "date.h"
+
+#include <type_traits>
+
+static_assert(std::is_same<decltype(date::last), const date::last_spec>{}, "");
+
+int
+main()
+{
+}