test: some tests stalls unexpectedly

[kenhys]

Problem

There are cases that test stalls.

Actual

If test is executed respectively, it will pass.

The following test cases tend to fail apparently, but it may vary on environment.

• test_watch_child_without_block
• test_nothing
• test_shift_jis_8bit
• test_raw_shift_jis_subject

run-test.sh v -n /.../ (specified each test) will succeed, so it may be affected by executing order.

Debian: sid
Ruby: ruby 2.7.5p203 (2021-11-24 revision f69aeb8314) [x86_64-linux] (installed via rvm)

Expected

All test pass.

[kou]

It seems that Process.waitpid is blocked when we use Milter::EventLoop#watch_child.

They are omitted or use Process.waitpid(pid, Process::WNOHANG) for now.