looks like you and @tkh44 thought of this at the same time, haha.
I left a comment on his PR: #352 (comment)

There's something funky going on with the prop-types lib when running in development mode where they've made it hard (impossible?) to validate manually, which is how preact-compat validates (as far as I know). Not sure if you were seeing this as well.

I'll take a look at this shortly - I'm running this successfully locally, but there's likely something I missed :-)

@developit I might be misunderstanding, but, the odd behavior I'm seeing is the result of the deprecation warning issued by this prop-types package when manually checking proptypes. This is documented in this article and shouldn't affect preact-compat since manual proptype checking only happens in dev and not production

Otherwise, I see tests passing that confirm this is working properly. Your jsfiddle also seems to check proptypes properly as long as you ignore that warning (I see valid resolve to true or false when I have valid and invalid proptypes)

That all being said - it's definitely not ideal to have deprecation warnings for supported behavior and that's enough to make me reconsider merging this. Feel free to merge in if you feel it's worth it, but I can always revisit this when React 16 comes out and the deprecation warning is removed

Edit: I do things a little differently than the other pull request, so you might experience different behavior across the two. Just a note :)

@developit This is way more comprehensive than my PR. Feel free to close #352

@developit not sure why tests are failing for components built with createClass() but this seems to be working pretty well for me locally on a project. No more sad deprecation warnings!

I've not tested createClass() locally, so, there's more to look into here. I'll see if I can get to it soon

Edit: Clarification