How to test that asyncio.Queue did NOT get something pushed

Question

I'm currently writing some async tests with pytest and found myself running into the following situation.

Consider we have an asyncio.Queue called peer2_subscriber that we want to check if it received a certain message (after triggering some action, omitted for brevity)

peer, cmd, msg = await asyncio.wait_for(
    peer2_subscriber.get(),
    timeout=1,
)

assert peer == peer2
assert isinstance(cmd, Transactions)
assert msg[0].hash == txs[0].hash

Now, consider that I want to test that another asyncio.Queue did NOT something pushed.

I found myself creating such a helper method.

async def wait_with_fallback(fn, fallback):
    try:
        return await asyncio.wait_for(
            fn(),
            timeout=1
        )
    except asyncio.TimeoutError:
        return fallback

And then in the test I write something like:

val = await wait_with_fallback(
    peer1_subscriber.get,
    None
)

assert val == None

I wonder if there's an existing pattern that I'm missing?

score 3 · Accepted Answer · answered Jun 18 '18 at 16:21

Your pattern works, so I would say it's "correct", for certain values of correct… It's mostly stylistic views here. I would write either

await asyncio.sleep(1)
assert peer1_subscriber.empty()

or

await asyncio.sleep(1)
val = peer1_subscriber.get_nowait()
assert val is None

How to test that asyncio.Queue did NOT get something pushed

1 Answers1