> C:/Users/Luis/Projects/oss/ruby/test/ruby/test_signal.rb:205: warning: cannot close fd before spawn
>
> And the second one stalls there until Ctrl+C is been hit, aborting the execution of other tests.
>
> test_signal.rb:205 (test_signal_requiring) specially excludes mswin and mingw tests, but seems is actually not being skipped.

Because, following line has typo.

    skip "limitation of GenerateConsoleCtrlEvent()" if /mswin|mignw/
=~ RUBY_PLATFORM

you need s/mignw/mingw/ fix. I think.
Unfortunately, I don't have mingw test environment. I hope you commit it.

Thanks.