Python 3.9.0a3+ (heads/master-dirty:f2ee21d858, Feb 19 2020, 23:19:22) 
[GCC 9.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import time
>>> time.sleep(-1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: sleep length must be non-negative
>>> import asyncio
>>> async def f():
...     await asyncio.sleep(-1)
...     print("no exception")
... 
>>> asyncio.run(f())
no exception

I think that also `asyncio.sleep()` should raise `ValueError` if the argument is less than zero.