io: test that mapped_file satisfies is_container_v

CMakeLists.txt

@@ -558,6 +558,7 @@ if (TESTS)
         hash/siphash
         hash/xxhash
         hton
+        io
         introspection
         iterator
         job/queue

test/io.cpp

@@ -0,0 +1,13 @@
+#include "tap.hpp"
+
+#include "io.hpp"
+#include "types/traits.hpp"
+
+
+///////////////////////////////////////////////////////////////////////////////
+int main ()
+{
+    cruft::TAP::logger tap;
+    tap.expect (is_container_v<cruft::mapped_file>, "mapped_file is a container");
+    return tap.status ();
+}