Whart was a watershed for me was when the very first version of PDK camne out, and I feel they at least kept this, the tests got all stubbed out, and they just worked. You didn't hve to go learn all the things about the various spec setup files, but you could pull up rspec-puppet.com and start testing right away. I never had anything remotely close to that success prior. It's nice to just get everything you need in a module right from the start when you type

pdk new module foo-bar

and have similar for creating classes

pdk new class bar::baz

that also create the test for you all stubbed out and ready to go. Replacing that functionality would be sweet.