Add unit tests for asyncio download methods

[fepas]

STONEBLD-1356

Maintainers will complete the following section

• Commit messages are descriptive enough
• Code coverage from testing does not decrease and new code is covered
• [n/a] Docs updated (if applicable)
• [n/a] Docs links in the code are still valid (if docs were updated)

[brunoapimentel]

Any chance we can also cover these lines? This would increase the coverage of this module to a good level.

Not sure how we'd do it though 🤔

[brunoapimentel]

Overall, great work 👍

Just left two minor comments.

[ben-alkov]

@fepas;

Coveralls reports missing coverage on LL110-113

[brunoapimentel]

LGTM!

We're still missing coverage in lines 110-113 and 113-139 because they proved quite tricky to test.

I believe the time we'd spend trying to get full coverage is probably not worth it, considering the main behavior is already covered.

[chmeliik]

LGTM 👍