Python 3.10: tests fail due to `DeprecationWarning: There is no current event loop`

[mgorny]

The test suite is failing against Python 3.10.0b1 due to a lot of DeprecationWarnings, e.g.:

==================================================================== FAILURES ====================================================================
________________________________________________________________ test_basic_async ________________________________________________________________
tests/test_async.py:29: in test_basic_async
    rv = run(func())
tests/test_async.py:17: in run
    loop = asyncio.get_event_loop()
E   DeprecationWarning: There is no current event loop
______________________________________________________________ test_await_on_calls _______________________________________________________________
tests/test_async.py:45: in test_await_on_calls
    rv = run(func())
tests/test_async.py:17: in run
    loop = asyncio.get_event_loop()
E   DeprecationWarning: There is no current event loop
_______________________________________________________ test_await_on_calls_normal_render ________________________________________________________
tests/test_async.py:58: in test_await_on_calls_normal_render
    rv = t.render(async_func=async_func, normal_func=normal_func)
.tox/py310/lib/python3.10/site-packages/jinja2/environment.py:1281: in render
    loop = asyncio.get_event_loop()
E   DeprecationWarning: There is no current event loop
[...]

To reproduce:

tox -e py310

Environment:

• Python version: 3.10.0b1
• Jinja version: ab78403

[davidism]

Using asyncio.run() should fix this, and will be possible when we drop Python 3.6 support in December. I guess if we want to avoid the warning before then we can replace get_event_loop with

if sys.version_info < (3, 7):
    loop = asyncio.get_event_loop()
    loop.run_until_complete(...)
else:
    asyncio.run(...)

[mgorny]

Thanks!