Normally most of the time I've just used CURL or the REST console Chrome plugin.
We've talked about it in the past, but there's nothing planned.
If you want to ensure that your code is working correctly you can use a tool such as VCR to build up a bunch of example requests and can replay those against your application during your tests. This should help you build up some good coverage. You may just want to also have a verification suite that asserts data hasn't changed (i.e different keys between your cassettes and what Shopify proper is rendering)