Test Runner: detect async issues for unittest.TestCase

[fornellas]

Python provides IsolatedAsyncioTestCase to run tests as async def test* methods. however, people often confuse this class with regular unittest.TestCase, and in such case, the test methods being coroutines, they will be called as if they were sync, never to be awaited, and tests will go green with no failures.

We already detect such cases (and others) for TestSlide's DSL tests. Lets update the test runner, so it can also detect such issues when running unittests.

Currently to detect async issues from TestSlide DSL we:

• Run the event loop with debug.
• Intercept log & warnings.

As long as the event loop is ran in debug, we can catch these. We can also add more patching to the event loop to not require debug (and perhaps an upstream patch for that as well). Eg: we could have at the event loop class level callbacks for async issues.

[fornellas]

I tested Python 3.7 & 3.8:

• With debug=False:
  • Both issue warning on not awaited coroutines.
  • None log slow execution.
• With debug=True:
  • Both log slow execution.

So, we can make the test runner itself intercept the forgotten await warning, neat.

For the slow execution, we can patch BaseEventLoop._run_once to set self._debug = True only when the method is running, so we can get this log message, without enabling debugging for everything.