Suppress pytest warnings due to test util classes

[cxong]

What do these changes do?

We are using pytest; by default it collects tests in:

• files that are named test_*.py
• classes that are named Test*

Unfortunately this matches the TestServer/TestClient classes in aiohttp. Since they have __init__() methods they won't break tests, but there will be warnings:

<path>/site-packages/aiohttp/test_utils.py:128
  <path>/site-packages/aiohttp/test_utils.py:128: PytestWarning: cannot collect test class 'TestServer' because it has a __init__ constructor
    class TestServer(BaseTestServer):

<path>/site-packages/aiohttp/test_utils.py:152
  <path>/site-packages/aiohttp/test_utils.py:152: PytestWarning: cannot collect test class 'TestClient' because it has a __init__ constructor
    class TestClient:

-- Docs: https://docs.pytest.org/en/latest/warnings.html

The easiest way would be to exclude these tests from pytest collection via __test__ = False. See https://stackoverflow.com/q/24614851/2038264

Are there changes in behavior for the user?

N/A

Related issue number

N/A

Checklist

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

Codecov Report

Merging #3660 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #3660      +/-   ##
=========================================
+ Coverage    97.9%   97.9%   +<.01%     
=========================================
  Files          43      43              
  Lines        8556    8558       +2     
  Branches     1376    1376              
=========================================
+ Hits         8377    8379       +2     
  Misses         74      74              
  Partials      105     105

Impacted Files	Coverage Δ
aiohttp/test_utils.py	99.35% <100%> (ø)	⬆️

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[codecov-io]

Codecov Report

Merging #3660 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #3660      +/-   ##
=========================================
+ Coverage    97.9%   97.9%   +<.01%     
=========================================
  Files          43      43              
  Lines        8556    8558       +2     
  Branches     1376    1376              
=========================================
+ Hits         8377    8379       +2     
  Misses         74      74              
  Partials      105     105

Impacted Files	Coverage Δ
aiohttp/test_utils.py	99.35% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7345ffb...a1406bd. Read the comment docs.

[asvetlov]

Cool!
I used to think that we have to rename these classes to avoid conflicts.
If __test__ = False solves the issue I happy to accept the PR!