Expand the nqp::encode/nqp::decode test.

t/nqp/82-decode.t

@@ -1,4 +1,4 @@
-plan(3);
+plan(5);
 
 class int8 is repr('P6int') {}
 class buf8 is repr('VMArray') {}
@@ -13,11 +13,27 @@ nqp::composetype(int16, nqp::hash('integer', nqp::hash('bits', 16)));
 nqp::composetype(buf16, nqp::hash('array', nqp::hash('type', int16)));
 
 my $buf := nqp::encode('', 'utf8', buf8.new);
-ok(1, 'encoding empty string as UTF-8');
+ok(nqp::elems($buf) == 0, 'encoding empty string as UTF-8');
 my $str := nqp::decode($buf, 'utf8');
-ok(1, 'decoding empty UTF-8 string into string');
+ok($str eq '', 'decoding empty UTF-8 string into string');
+
 
 # Test for a regression in the Parrot backend.
 $buf := nqp::encode('a', 'utf16', buf16.new);
 $str := nqp::decode($buf, 'utf16');
-ok(1, 'round-tripping via UTF-16');
+ok($str eq 'a', 'round-tripping via UTF-16');
+
+my $hello := nqp::encode('Hello World', 'utf8', buf8.new);
+
+sub buf_dump($buf) {
+  my @parts;
+  my $i := 0;
+  while $i < nqp::elems($buf) {
+    @parts.push(~nqp::atpos_i($hello, $i));
+    $i := $i + 1;
+  }
+  nqp::join(",", @parts);
+}
+
+ok(buf_dump($hello) eq "72,101,108,108,111,32,87,111,114,108,100", "Hello World is encoded to utf8 correctly");
+ok(nqp::decode($hello, "utf8") eq "Hello World", "round-tripping Hello World");