cmake build test error on macOS

[leafok88]

During build / test from source (version 3.3.6) with CMake on macOS, 1 of 33 tests failed. The error message was as below.

32/33 Test #34: test_event .......................Subprocess aborted***Exception: 0.01 sec
Assertion failed: (bind(fd, (struct sockaddr *)&address, sizeof(address)) == 0), function main, file test_event.c, line 56.

  Start 35: test_resolv_async

97% tests passed, 1 tests failed out of 33

The following tests FAILED:
34 - test_event (Subprocess aborted) unit
Errors while running CTest

The command executed:
cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build --parallel
ctest --test-dir build -L 'unit|vendor' --output-on-failure

Testing environment:
cmake version 4.4.3
Darwin Kernel Version 25.6.0: arm64

[madeye]

Thanks for the report. This is caused by macOS's default per-process file descriptor limit rather than a bug in the event loop.

test_event deliberately opens 256 UDP sockets (to exceed Winsock's 64-descriptor select() limit) plus a sender socket and the loop's own kqueue descriptor. A stock macOS Terminal session starts with a soft limit of 256 (ulimit -n prints 256), so socket() starts returning -1 near the end of that loop and the unchecked descriptor trips the bind() assertion you saw. Running with a higher limit already makes the test pass on 3.3.6:

ulimit -n 1024
ctest --test-dir build -L 'unit|vendor' --output-on-failure

#3060 fixes this properly: CTest now raises the soft limit to 1024 before launching each unit test, test_event raises its own limit when run directly, and a socket() failure is now reported as such instead of as a bind() failure.