running make test-all the error I get is:
  1) Failure:
test_kernel_open(PathnameTest)
    [C:/ruby-build/ruby/lib/pathname.rb:1197:in `test_kernel_open'
     C:/ruby-build/ruby/lib/pathname.rb:1195:in `open'
     C:/ruby-build/ruby/lib/pathname.rb:1195:in `test_kernel_open']:
<2> expected but was
<0>.


ruby -v 
ruby 1.9.0 (2005-01-05) [i386-mingw32]
gcc -v
Reading specs from C:/Programmi/msys/MinGW/bin/../lib/gcc/mingw32/3.4.2/specs
Configured with: ../gcc/configure --with-gcc --with-gnu-ld --with-gnu-as --host=
mingw32 --target=mingw32 --prefix=/mingw --enable-threads --disable-nls --enable
-languages=c,c++,f77,ada,objc,java --disable-win32-registry --disable-shared --e
nable-sjlj-exceptions --enable-libgcj --disable-java-awt --without-x --enable-ja
va-gc=boehm --disable-libgcj-debug --enable-interpreter --enable-hash-synchroniz
ation --enable-libstdcxx-debug
Thread model: win32
gcc version 3.4.2 (mingw-special)

on winxp pro (athlon 2000+) 

Date: 2008-11-09 04:20
Sender: Roger Pack

you may be able to overcome it [if it's a file writing problem]
by using file_instance.fsync
If it's still a problem please re-submit to the new tracker
http://redmine.ruby-lang.org/
this one's being shelved.
Thanks!
-=R

Date: 2008-11-08 01:28
Sender: Roger Pack

seems that make test [at least] passes now with mingw

Date: 2005-01-05 00:16
Sender: Usaku Nakamura

Logged In: YES 
user_id=1531

It's known, but not fixed yet.
(This is MSVCRT's problem.)