Run existing test suites

[KarelPeeters]

Test sources:

• onnx backend test
• maybe onnxruntime has its own extended test set?

Sadly this might require giving up on the symbolic batch_size concept, at least for ONNX loading 😞.

[KarelPeeters]

With https://github.com/KarelPeeters/Kyanite/issues/1 this might actually be really easy, just define a new onnx backend around the Kyanite python wrapper and use that to run the tests!

[KarelPeeters]

https://github.com/onnx/onnx/blob/main/docs%2FImplementingAnOnnxBackend.md

[KarelPeeters]

Try loading all the models in the ONNX model zoo: https://github.com/onnx/models

Also look at the related project: https://github.com/onnx/turnkeyml