xo-unit: test: verify natural_unit/scaled_unit is structural type

utest/natural_unit.test.cpp

@@ -0,0 +1,37 @@
+/* @file natural_unit.test.cpp */
+
+#include "xo/unit/natural_unit.hpp"
+#include <catch2/catch.hpp>
+
+namespace xo {
+    namespace qty {
+        using nu64_type = natural_unit<std::int64_t>;
+
+        /* compile-time test:
+         * verify we can use an nu64_type instance as a non-type template parameter.
+         * Will need this for quantity<Repr, Int, natural_unit<Int>>
+         */
+        template <nu64_type nu>
+        constexpr nu_abbrev_type nu_mpl_abbrev = nu.abbrev();
+
+        TEST_CASE("natural_unit", "[natural_unit]") {
+            //constexpr bool c_debug_flag = false;
+
+            // can get bits from /dev/random by uncommenting the 2nd line below
+            //uint64_t seed = xxx;
+            //rng::Seed<xoshio256ss> seed;
+
+            //auto rng = xo::rng::xoshiro256ss(seed);
+
+            //scope log(XO_DEBUG2(c_debug_flag, "TEST_CASE.bpu"));
+            //log && log("(A)", xtag("foo", foo));
+
+            static_assert(nu_mpl_abbrev<nu::gram> == nu::gram.abbrev());
+            REQUIRE(nu_mpl_abbrev<nu::gram> == nu::gram.abbrev());
+
+        } /*TEST_CASE(natural_unit)*/
+    } /*namespace qty*/
+} /*namespace xo*/
+
+
+/* end natural_unit.test.cpp */