This needs closer inspection, but here are some things that currently do not work, either at the parser level, or at actual deployment time:
xd:>module compose foo --definition "queue:bar > filter"
Command failed org.springframework.xd.rest.client.impl.SpringXDException: Could not find module with name 'filter' and type 'sink'
xd:>module compose foolog --definition "queue:foo > log"
Successfully created module 'foolog' with type sink
==> should fail (not a module, but a full stream)
xd:>module compose foo --definition "queue:bar > filter | transform"
Successfully created module 'foo' with type processor
==> should be source