IO#close_on_exec? is not supported on MinGW
MODIFY
mrbgems/mruby-io/test/io.rb
mrbgems/mruby-io/test/io.rb
@@ -216,7 +216,10 @@ assert('IO#dup for readable') do
dup = io.dup
assert_true io != dup
assert_true io.fileno != dup.fileno
+ begin
assert_true dup.close_on_exec?
+ rescue NotImplementedError
+ end
assert_equal 'm', dup.sysread(1)
assert_equal 'r', io.sysread(1)
assert_equal 'u', dup.sysread(1)

IO#close_on_exec? is not supported on MinGW