encoding: make Block convertible to span

Change-Id: Idb501467d1c56b95e7fdb76acda63b919fe98f85
diff --git a/tests/unit/security/additional-description.t.cpp b/tests/unit/security/additional-description.t.cpp
index 56a9090..2779816 100644
--- a/tests/unit/security/additional-description.t.cpp
+++ b/tests/unit/security/additional-description.t.cpp
@@ -72,10 +72,7 @@
   it++;
   BOOST_CHECK(it == aDescription.end());
 
-  BOOST_CHECK_EQUAL_COLLECTIONS(aDescription.wireEncode().wire(),
-                                aDescription.wireEncode().wire() + aDescription.wireEncode().size(),
-                                DESC,
-                                DESC + sizeof(DESC));
+  BOOST_TEST(aDescription.wireEncode() == DESC, boost::test_tools::per_element());
 
   AdditionalDescription aDescription2(Block{DESC});
   BOOST_CHECK_EQUAL(aDescription2, aDescription);