Not to say that DotA wouldn't benefit from more rigorous testing, but in Valve's defense I'd say that the complexity of interactions in DotA is far beyond LoL. Some of the bugs you're seeing might only arise in extremely rare situations.

DotA is balanced with creativity in mind. When an exploitative strategy is found the game is not changed to remove it but instead through some combination of tweaks and modifications, often to seemingly unrelated aspects it's made into something that's only situationally viable.

The reason the game is so deep/interesting is because this philosophy has been in place for many (10+) years now resulting in a game that's much more complex than pretty much anything else out there. DotA 2 retains edge case behavior that was present in the original Warcraft 3 mod. Things that were once engine limitations are now part essential parts of gameplay. Preserving these weird interactions instead of attempting to make the game more regular/comprehensible is one of the things that allows such a high level of creativity in competitive play. There's always a way you can outplay your opponent that's clever. In go parlance: there's always new tesuji to be found.

All that being said I think Riot's efforts here are quite laudable and DotA could certainly find benefit from more rigorous testing.

This is a silly comment. A cursory search of "League of Legends Bugs" yields similar results, lots of bugs. In fact, the Mac Client was rendered completely unplayable less than a month ago, which may have been fixed by now. Valve employ people that build automated testing (which very well may have built a system used by Dota 2 devs), so I think your last statement could be incorrect, but either way it is speculation, unless you have a source for that.

Maybe we extend the benefit of the doubt and perceive the comment as a reminder that having code that passes all the tests doesn't necessarily equate to having a good product?

It's obviously a stretch as that guy's username is the name of a DotA hero, but hey, rose colored glasses are fun sometimes.

i dunno i keep reading on the dota 2 subreddit how riot is ruining LoL and new players asking for advice.