With this PR, the test is now skipped on FreeBSD:

$ ./python -m test test_cmd_line_script -v -m test_script_as_dev_fd
(...)
test_script_as_dev_fd (test.test_cmd_line_script.CmdLineTest.test_script_as_dev_fd) ... skipped 'Requires fdescfs mounted on /dev/fd on FreeBSD'

If I mount manually /dev/fd, it works as expected:

$ sudo mount -t fdescfs none /dev/fd 

$ ./python -m test test_cmd_line_script -v -m test_script_as_dev_fd
(...)
test_script_as_dev_fd (test.test_cmd_line_script.CmdLineTest.test_script_as_dev_fd) ... 

/usr/home/vstinner/python/main/Lib/subprocess.py:849: RuntimeWarning: pass_fds overriding close_fds.
  warnings.warn("pass_fds overriding close_fds.", RuntimeWarning)

ok
(...)

cc @ronaldoussoren

By the way, the test emits a warning because of this Lib/subprocess.py code:

            if pass_fds and not close_fds:
                warnings.warn("pass_fds overriding close_fds.", RuntimeWarning)
                close_fds = True

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.11.
🐍🍒⛏🤖

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.10.
🐍🍒⛏🤖

Sorry, @vstinner, I could not cleanly backport this to 3.10 due to a conflict.
Please backport using cherry_picker on command line.
cherry_picker 038b151963d9d4a5f4c852544fb5b0402ffcb218 3.10

GH-100007 is a backport of this pull request to the 3.11 branch.

Ah, test_script_as_dev_fd() was not backported to Python 3.10.

It was, in #99817.
This fails on the stable buildbot, so it should be backported to 3.10 & 3.9.

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.9.
🐍🍒⛏🤖

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.10.
🐍🍒⛏🤖

Sorry, @vstinner, I could not cleanly backport this to 3.9 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 038b151963d9d4a5f4c852544fb5b0402ffcb218 3.9

GH-125109 is a backport of this pull request to the 3.10 branch.