Add S3 tests for uploading files.

[FledgeXu]

So far, we haven't tested the S3 upload file part, we need to add this part of the test

[rgaudin]

The S3 upload is not tested but some higher level tests depend on S3 so the upload code is run in tests. This is problematic because it requires valid S3 URL/credentials to run tests.

We also have tests mocking S3.

This ticket should thus:

• create independent Upload-testing test that require a valid URL and are run conditionally via a mark.
• use mocked S3 for all other tests so by default S3 URL is not required for tests