Use aiohttp fixtures

[Olegt0rr]

What do these changes do?

Simplify tests with aiohttp fixtures

Are there changes in behavior for the user?

No changes

Related issue number

Closes #447

Checklist

• [x] I think the code is well written
• [x] Unit tests for the changes exist
• [x] Documentation reflects the changes

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (033615e) 100.00% compared to head (2a54692) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #453 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 4 4 Lines 480 436 -44 Branches 52 52 ========================================= - Hits 480 436 -44 ```

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