I am implementing databases in hardware, means - pure silicon - and i know, how hard that is!
I am following Dgraph now for a while and here are my 2¢:
Test driven development must vastly improve in Dgraph, Badger. I think, Dgraph could massively improve by introducing kind of collective test set. The art of TDD always is in generating test data, of course. Perhaps we all could contribute more, much more here.