Ensure TestClient HTTP methods return a context manager

[alexhayes]

What do these changes do?

A user should be able to run a test as per the client documentation;

async with aiohttp.ClientSession() as session:
    async with session.get('https://api.github.com/events') as resp:
        print(resp.status)
        print(await resp.text())

However, because the test client doesn't return a context manager the above does not work (unless of course I'm doing something wrong).

This PR ensures the HTTP methods on TestClient return a context manager so that it mimics the same interface as a non-test client

Are there changes in behaviour for the user?

Yes, the TestClient will behave the same as the non-test client that their code will be using :)

Let's say or instance your code looked as follows;

# client request code
async request_hello(session):
    async with session.get('...') as resp:
        ...

Note the use of the context manager: async with session.get('...') as resp:

And your test was;

# pytest
from aiohttp import web

async def hello(request):
    return web.Response(text='Hello, world')

async def test_hello(test_client, loop):
    app = web.Application(loop=loop)
    app.router.add_get('/', hello)
    client = await test_client(app)
    resp = await request_hello(client)
    assert resp.status == 200
    ...

On master, this would fail, because TestClient does not return a context manager.

Related issue number

None.

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• Add yourself to CONTRIBUTORS.txt
• Add a new entry to CHANGES.rst

[codecov-io]

Current coverage is 98.51% (diff: 100%)

Merging #1318 into master will increase coverage by <.01%

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  Methods           0          0          
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  Branches       1094       1094          
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+ Hits           6418       6419     +1   
  Misses           47         47          
  Partials         50         50          

Powered by Codecov. Last update 0033c48...9a40cc8

[asvetlov]

Please resolve conflict in CHANGES.rst.
I'll merge the PR after this.

[alexhayes]

Rebased master onto my branch and force pushed.

[asvetlov]

Cool! Thanks!

[lock]

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