Test sometimes was failed and sometimes works well

[matsumotory]

for i in `seq 10`; do rake test | grep "Total\|OK:\|KO:" >> result ; done

Total: 878
   OK: 876
   KO: 2
Total: 878
   OK: 875
   KO: 3
Total: 878
   OK: 877
   KO: 1
Total: 878
   OK: 875
   KO: 3
Total: 878
   OK: 872
   KO: 6
Total: 878
   OK: 877
   KO: 1
Total: 878
   OK: 877
   KO: 1
Total: 878
   OK: 878
   KO: 0
Total: 878
   OK: 878
   KO: 0
Total: 878
   OK: 876
   KO: 2

mruby hash is 91ba9ba. This issue was reproduced on CentOS6 and MacOSX for now.