There are different "bests" for different kinds of feedback, I suppose. If you have something that's pretty much certainly a bug, bugs-parrot at bugs6.perl.org is probably the best target (bugs-perl6 may also be up and running). If you have a patch, adding "[PATCH]" to the subject tags it automatically.

If you're not sure whether or not something should work, you can email either me (Sean) or perl6-internals with the question. If you want to make something work (i.e. by implementing it), I'm probably the one you should be bugging, since it will encourage me to document things.

If something clearly isn't implemented, a test-case is probably overkill -- just note it as "not implemented" and I'll put it somewhere in the docs. Hyper-assignment falls into this category. If something looks like it should work, but doesn't, then a test case is probably more appropriate.

Both of the tests you provide above look good overall, though I'm not sure about some of the cases in the second. For example,

       print "--" _ (@a ^_ "\t");      # BAD: --
[download]

is concatenating "--" with an array value. It should probably evaluate the array in scalar context (yielding its length) instead of turning into an empty array, but I don't think it will be expanded as in double-quoted string context.

/s