Improve message tests

[Brian Curtin]

Several tests of the message proxy require a departure from the standards we're able to apply elsewhere around the proxies as the message proxy methods often don't pass through the proxy base class. We should probably introduce a subclass of the proxy verification methods that can be written once and applied throughout the message tests.

[Terry Howe (thowe-g)]

It also makes me wonder if move of the work should be done at the resource level instead. I know messaging is different and this may not be possible.