Golden Testing a CAD Library

A Haskell developer behind the open-source CAD tool Waterfall-CAD has finally tackled a problem that had been nagging him for years: how do you test software that spits out 3D models? His answer was surprisingly relatable — stop treating the result like a mysterious math object and start treating it like a picture. By leaning on SVG image output and so-called “golden tests,” he’s basically comparing today’s drawing to yesterday’s drawing and sounding the alarm if they don’t match.

But the real action was in the replies, where the community instantly turned into a panel of backseat engineers. One commenter was politely supportive, but others showed up with the classic internet energy of “cool idea, now here’s how I’d do it better.” One person pushed an image-diff tool and argued that if the files are already vector drawings, comparing the raw SVG first would be smarter and cheaper than saving loads of image files. Another commenter rolled in with big veteran energy, basically saying, “we’ve had tools for this forever.” And then things got delightfully nerdy: someone suggested checking whether exported 3D shapes keep the same volume after being saved and loaded again — a very serious-sounding way of saying, “make sure your digital object still weighs what it should.”

There was even a wild side quest into whether large language models — the AI systems behind chatbots — could someday speed-run circuit and machine design. So yes, the post was about testing drawings, but the comments turned it into a mini-drama about the right way to prove a machine-made shape is real.