Use a pytest or other library method to generate the verbose assertion error instead of hardcoding the exception message in the unit test

[gokulavasan]

Example of this https://github.com/pytorch-labs/torchtune/blob/main/tests/torchtune/utils/test_env.py#L73-L76

Creating this issue as an follow from this comment - #193 (comment)

[kartikayk]

Closing this since we recently discussed best practices for tests and are tracking this elsewhere.