Jamba: revert skipped test

[gante]

What does this PR do?

Fixes #30828 🤗

Jamba: reverts skipped test, it is now passing on main
Mamba: all_generative_model_classes is not set on Mamba's tests, as it requests the attention outputs in the generate calls (which mamba doesn't have). Added a comment regarding that on MambaModelTest

(feel free to merge if you approve)

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[amyeroberts]

Just so I understand, are mamba and jamba generative models? I thought so. Is there a reason why we can't have custom generative tests for these models which don't require attention?

[gante]

@amyeroberts both are generative.

Jamba has the generative tests enabled (it has attention outputs):

transformers/tests/models/jamba/test_modeling_jamba.py

Line 289 in 5c88253

all_generative_model_classes = (JambaForCausalLM,) if is_torch_available() else ()

Mamba doesn't have. I agree it would be nice to have some tests -- or better yet, for the tests to be more flexible, don't check attention if the model doesn't have attentions. Would you be okay with a) adding a TODO in the code; b) opening an issue to make the tests more flexible?

[amyeroberts]

Would you be okay with a) adding a TODO in the code; b) opening an issue to make the tests more flexible?

@gante In this case no. As mamba is pretty popular, has very unusual logic, this isn't just something flaky e.g. hardware, and generates we should be testing its generation logic properly