[tests][dask] make find-open-port test more reliable

[jameslamb]

Working on a proposal to address #3823 (review), I found that sometimes the "find an open port" test in test_dask.py failed with an error.

assert new_port == 12401
E assert 12404 == 12401

I think that test is too strict. Right now it checks "if port 12400 is unavailable, _find_open_port() returns 12401". If 12401 is busy for some unrelated reason, this test fails.

This PR proposes loosening the condition a bit, to reduce the risk of test failures like that. It isn't important that that method finds 12401 specifically. Just some port that is > the port number you passed in.

[StrikerRUS]

I think that test is too strict.

I think now test is too soft 😃 . What about checking some meaningful intervals? Something like

worker_ip = '127.0.0.1'
port = listen_port
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.bind((worker_ip, port))
    ...
assert port < new_port < port + 10

[jameslamb]

ok I can change it to port < new_port < port + 1000, since that is the range that the function covers:

LightGBM/python-package/lightgbm/dask.py

Line 72 in 5321fef

max_tries = 1000

[StrikerRUS]

Thanks!

[github-actions]

This pull request has been automatically locked since there has not been any recent activity since it was closed. To start a new related discussion, open a new issue at https://github.com/microsoft/LightGBM/issues including a reference to this.