aiotime

An asyncio test helper that allows you to deterministically control the event loop's internal clock in your tests, affecting the behavior of the following functions:

1. asyncio.sleep
2. loop.call_at
3. loop.call_later

Note about behavior

If you enter the aiotime.FastForward context manager (as in the with block in the examples below), then the loop supplied to its constructor will STOP triggering scheduled events, tasks or callbacks. Once you __enter__ the context manager, you MUST call the returned object or the event loop will be stuck in time. Only when you __exit__ the context manager will the loop return to normal behavior.

(Using the same event loop with and without aiotime control is not supported; there may be unexpected effects with scheduling at the margins.)

Getting started

pip install aiotime
python
>>> import aiotime

Controlling asyncio.sleep

loop = asyncio.get_event_loop()

# Try sleeping with normal loop behavior
start = dt.datetime.now()
sleep_task = asyncio.create_task(asyncio.sleep(0.25))
await sleep_task
assert dt.datetime.now() - start > dt.timedelta(seconds=0.25)

with aiotime.FastForward(loop) as ff:
    # Try fast-forwarding through the sleep
    start = dt.datetime.now()
    sleep_task = asyncio.create_task(asyncio.sleep(0.25))
    await ff(1.5)  # ff more than necessary
    await sleep_task
    assert dt.datetime.now() - start < dt.timedelta(seconds=0.05)

Controlling loop.call_later

loop = asyncio.get_event_loop()

with aiotime.FastForward(loop) as ff:
    # Try call_later() with fast-forwarding
    start = dt.datetime.now()
    event = asyncio.Event()
    def test():
        event.set()
    loop.call_later(0.25, test)
    await ff(1.5)  # ff more than necessary
    await asyncio.wait_for(event.wait(), 2)  # timeout just in case
    assert dt.datetime.now() - start < dt.timedelta(seconds=0.05)

# call_later() with normal loop behavior now, after context manager exits
start = dt.datetime.now()
event = asyncio.Event()
def test():
    event.set()
loop.call_later(0.25, test)
await asyncio.wait_for(event.wait(), 1)  # timeout just in case
assert dt.datetime.now() - start > dt.timedelta(seconds=0.25)