[Good first issue] LXMERT TensorFlow Integration tests

[LysandreJik]

The TensorFlow implementation of the LXMERT model currently has no integration tests. This is problematic as the behavior can diverge without being noticed.

The test_modeling_tf_lxmert.py file should be updated to include integration testing.

An example of a good modeling integration test is visible in the test_modeling_tf_bert.py#L365-L387 file:

https://github.com/huggingface/transformers/blob/1809de5165804666ba6c6a02a9d177f6683869cc/tests/test_modeling_tf_bert.py#L365-L387

Some additional tips:

• The test must be marked as slow using the @slow decorator, so as to be run daily, and not on every commit of every branch/pull request of this repository.
• The test must be decorated with the @require_tf decorator so as to only be run in environments using PyTorch.
• A single test is necessary. If you feel like implementing multiple of these, then sharing the same checkpoint would be ideal so as to reduce download time.

[PradipNichite]

@LysandreJik is anyone working on it? I would like to work.

[LysandreJik]

Hi! @sadakmed already has a close to finished implementation that we'll merge in the coming days.

Thank you for offering to contribute!

[AkechiShiro]

Hi, shouldn't this issue be closed now ? Since a valid integration test was merged ?

[LysandreJik]

Yes, it should :) Thanks!