qa: Failure in wallet_basic.py spendzeroconfchange test #32456

CI failure (job: "macOS 14 native, arm64, no depends, sqlite only, gui") upon merge of my PR (ad5cd129f3cc72f2d2b140e182781bf3bb5dbacc): https://github.com/bitcoin/bitcoin/actions/runs/14916001314/job/41901630172

Relevant high-level log:

22/267 - wallet_basic.py failed, Duration: 23 s

stdout:
2025-05-08T21:04:47.763000Z TestFramework (INFO): PRNG seed is: 1820560705145373934
2025-05-08T21:04:47.764000Z TestFramework (INFO): Initializing test directory /Users/runner/work/bitcoin/bitcoin/ci/scratch/test_runner/test_runner_₿_🏃_20250508_210317/wallet_basic_241
2025-05-08T21:04:49.006000Z TestFramework (INFO): Mining blocks...
2025-05-08T21:04:50.323000Z TestFramework (INFO): Test gettxout
2025-05-08T21:04:50.342000Z TestFramework (INFO): Test gettxout (second part)
2025-05-08T21:04:56.786000Z TestFramework (INFO): Test sendmany
2025-05-08T21:04:56.833000Z TestFramework (INFO): Test sendmany with fee_rate param (explicit fee rate in sat/vB)
2025-05-08T21:04:56.873000Z TestFramework (INFO): Test sendmany raises 'fee rate too low' if fee_rate of 0.99999999 is passed
2025-05-08T21:04:56.876000Z TestFramework (INFO): Test sendmany raises if an invalid fee_rate is passed
2025-05-08T21:04:56.894000Z TestFramework (INFO): Test sendmany raises if an invalid conf_target or estimate_mode is passed
2025-05-08T21:04:59.702000Z TestFramework (INFO): Test -walletbroadcast
2025-05-08T21:05:06.265000Z TestFramework (INFO): Test -reindex
2025-05-08T21:05:08.464000Z TestFramework (INFO): Testing gettransaction response with different arguments...
2025-05-08T21:05:08.468000Z TestFramework (INFO): Test send* RPCs with verbose=True
2025-05-08T21:05:08.475000Z TestFramework (INFO): Test send* RPCs with verbose=False
2025-05-08T21:05:08.480000Z TestFramework (INFO): Testing 'listunspent' outputs the parent descriptor(s) of coins
2025-05-08T21:05:08.499000Z TestFramework (INFO): Test -spendzeroconfchange
2025-05-08T21:05:09.800000Z TestFramework (ERROR): Assertion failed
Traceback (most recent call last):
  File "/Users/runner/work/bitcoin/bitcoin/test/functional/test_framework/test_framework.py", line 183, in main
    self.run_test()
    ~~~~~~~~~~~~~^^
  File "/Users/runner/work/bitcoin/bitcoin/ci/scratch/build-aarch64-apple-darwin23.6.0/test/functional/wallet_basic.py", line 659, in run_test
    assert_equal(len(utxos), 1)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^
  File "/Users/runner/work/bitcoin/bitcoin/test/functional/test_framework/util.py", line 77, in assert_equal
    raise AssertionError("not(%s)" % " == ".join(str(arg) for arg in (thing1, thing2) + args))
AssertionError: not(0 == 1)

So far unable to reproduce on NixOS. Among other things tested:

build/test/functional/wallet_basic.py --random=1820560705145373934
build/test/functional/test_runner.py --ci -j25 --tmpdirprefix /tmp/test_runner/ --ansi --combinedlogslen=99999999 --timeout-factor=40 --quiet --failfast

Edit: Next push to master succeeded as l0rinc noted, so this seems possibly timing dependent/racy.

I can't reproduce it either on my Mac - but it does seem to be passing with latest push at least.

<img width="549" alt="Image" src="https://github.com/user-attachments/assets/30b441f9-a8d0-44ff-b23c-2529a7de424a" />

See #32483 for a fix / way to reproduce.

@mzumsande thanks for fixing this! Sorry I didn't have the time to fully understand how the wallet syncs before the fix was merged.