the model for UniqueOp in backend test is not always correct for different input

[chentong319]

Bug Report

Is the issue related to model conversion?

No

Describe the bug

The shape of the output tensors for Unique Op is input content dependent. However, the model generated by backend test, for example, test_unique_sorted_without_axis, is given a constant shape to the outputs based on the value of the given inputs in the test. Is it possible to generate dynamic shape for the outputs of Unique?

System information

onnx version: 1.17.0

Reproduction instructions

Check the file: onnx/onnx/backend/test/case/node/unique.py

Expected behavior

Notes