Fixing offline mode for pipeline (when inferring task).
Author: Narsil
Pull request: yes

# What does this PR do?


```pyton
pipe = pipeline(model="xx")
```

Was actually using network even when `TRANSFORMERS_OFFLINE=1` was used.

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Fixes # (issue)


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Comments:
_The documentation is not available anymore as the PR was closed or merged._

> So the current `test_offline_mode` should be split in two, with one test just doing TRANSFORMERS_OFFLINE=1 and somehow testing there are no calls to the Hub, and a second test `test_cached_is_used_when_offline` where we do the mock but don't touch TRANSFORMERS_OFFLINE. The test you're adding should be like `test_offline_mode` and not mock anything (unless it's to check there are no calls to the internet).

For the added test this is indeed the only thing proving it fails when the code doesn't check the offline mode.

For the other tests if I understand correctly it's `TRANSFORMERS_OFFLINE=1` -> Users asks us to not touch internet, regardless of if internet is available or not. We should FAIL if we're hitting the internet (hence the mock).

If internet is not available, regardless of `TRANSFORMERS_OFFLINE` we should default to the cached version.

That's ok for the `from_pretrained` but I don't think this is doable with the pipeline task, because it's not included directly in the model + config, right ? Only the README.md has that information, of which we do not have a cached version, correct ? (Don't think we should either).

If that's correct, then I'm ok with splitting the tests, but the mock should still probably be in both tests, 1 to fake a buggy internet, the other to make sure we trigger an failure when we actually use internet even after been explicitly asked not to do it, no ?

(We could change the mock errors strings to reflect that difference)

Agreed! And yes the pipeline task for those tests needs to be passed, it can't be retrieved in offline mode/internet fails.

Made the changes is that what you had in mind ?