[v6.d REVIEW] Improve Encoding::Registry.find tests

Actually test it found the right encoding instead of giving us any
ol' Encoding object.

Orig: c8f9fa490

S32-encoding/registry.t

@@ -1,13 +1,20 @@
 use Test;
+use lib $?FILE.IO.parent(2).add: 'packages';
+use Test;
+use Test::Util;
 
 plan 15;
 
-ok Encoding::Registry.find('utf8') ~~ Encoding, 'Can find built-in utf8 encoding';
-ok Encoding::Registry.find('utf-8') ~~ Encoding, 'Can find built-in utf-8 encoding';
-ok Encoding::Registry.find('UTF-8') ~~ Encoding, 'Can find built-in UTF-8 encoding';
-ok Encoding::Registry.find('ascii') ~~ Encoding, 'Can find built-in ascii encoding';
-ok Encoding::Registry.find('iso-8859-1') ~~ Encoding, 'Can find built-in iso-8859-1 encoding';
-ok Encoding::Registry.find('latin-1') ~~ Encoding, 'Can find built-in latin-1 encoding';
+for <utf8  utf-8  UTF-8  ascii  iso-8859-1  latin-1> -> $name {
+    group-of 3 => "Can find built-in $name encoding" => {
+        given Encoding::Registry.find: $name {
+            isa-ok  $_, Encoding::Builtin, 'type of result';
+            does-ok $_, Encoding, 'does Encoding role';
+            is (.alternative-names, .name).flat».fc.any, $name.fc,
+                'found right encoding';
+        }
+    }
+}
 
 throws-like { Encoding::Registry.find('utf-29') },
     X::Encoding::Unknown, name => 'utf-29',