Expand notes on test cases

TODO

@@ -3,4 +3,16 @@ a mistake.
 
 Tests needed:
  - encode and decode of each kind of RR
+    - so far, have: txt, a, ns, mx, soa, cname, aaaa, srv.
+    - that leaves: md, mf, mb, mg, mr, null, wks, ptr, hinfo, minfo
+    - most of those are obsolete, so finding wild examples will be
+      very difficult
+
  - encode and decode of several variants of packet, both sensible and not
+    - misleading section length count - short, long
+    - misleading label length - short, long
+    - misleading rdata length - short, long
+    - misleading txt record string length - short, long
+    - looping domain-name (using compressed format)
+    - compressed domain-name pointing into hyperspace
+    - txt record with rdata filled with a list of empty byte-strings